HOW TO OBTAIN THE OVERRIDE FREQUENCIES FOR THE SLEEPER NODES
Too unlock these Sleeper Nodes - they're the same as the ones from the Arecibo Adventure on Io - you need to:
Complete the DLC main story and then complete the subsequent blue Ana missions on Mars to unlock the Nascent Dawn 1/5 Pursuit.
Complete 3 patrols and then complete a Lost Sector to acquire 4 Resonant Stems which you can combine into an Override Frequency for a specific music box to complete the Nascent 1/5 quest item.
The last 3 words of the Override Frequency item will give you a clue as to where the music box is located (and these key words are included in the list below).
Return to Ana and complete the new Diary 1/5 quest item by putting a thing you get from Ana into a thing near Ana to get a lore thing.
To obtain more Resonant Stems complete Patrols, Public Events (2 stems from Heroic PEs), Lost Sectors or loot the chests from high value targets - Ilheru Xolborne in the Glacial Drift, Yer'ot The Forgottenand a Cabal in the Braytech Futurescape.
I have found that the most efficient farming for Resonant stems is to continually complete patrol missions (they're all pretty quick except for the Psion collectable one) and complete Heroic Public events (2 stems each) and kill high level targets whenever they are available - make sure to complete the killing/gathering patrols during PEs and one of the traveling patrols when you are going for a Sleeper Node.
The rewards from each music box are random and usually include shaders and some sort of engram. I did get a "Braytech Schematic" from the 2nd one I opened (likely random) which can be turned in for a "Warmind Engram" which looks to be another type of Powerful Gear engram that can be used for the hard cap level grind.
With the First Sleeper Simulant acquired, it appears you don't need to complete all 40 of the Sleeper Nodes to unlock the gun, only 15 nodes need to be turned in as one of the steps on the IKELOS weapon quest. Now I wonder what completing all 40 will do, my guess is an ornament but we won't know until we know.
Just figured I'd put together a list of the cubes that require an override frequency for posterity once we can get those. Will continually update as new ones are added, feel free to help out.
The first picture is the location of your cursor/marker on the map, the second shows a picture of the surroundings. They are roughly in the order you would encounter them in those areas.
Descent.Cavern.Warsat - On a ledge just below the entrance to the PAVONIS 45 cache.
Descent.Chasm.Ledge - On a lower ledge on the south side of the large cave area by the Glacial Drift.
Descent.Caves.Runes - Just to the left of the entrance to the Penumbral Depths, which is blocked by a Hive door (initially, anyway).
Drift.Subterrane.Cliffside - On the left side just before you enter the Ma'adim Subterrane Lost Sector.
Drift.Transit.Freight - In a partially open container on the bridge.
Drift.Gatehouse.Catwalk. - In the building at the NW end of the bridge with the train tracks, up on the left catwalk behind the pillar. There is a region chest at the other end of the catwalk.
Drift.Transit.Foundation - Under the bridge on the NW end of the bridge.
Drift.Service.BackEnd - In the building on the way to the Braytech Futurescape, on the right side.
Drift.Checkpoint.Elevator - In the "C-67" Building on the SW end of the train track bridge, in the left room.
Drift.Flammable.Storage - In the left of the small building on the other side of the mountain from the SW end of the train tracks.
X.X.X. - Across from where you enter the Alton Dynamo in the wide open frozen area.
Drift.Subterrane.Chasm - In the Ma'adim Subterrane Lost Sector, under the thin bridge that leads the the 2nd area.
X.X.X. - In the Ma'adim Subterrane Lost Sector, after you cross the thin bridge to the 2nd area with Cabal.
Dynamo.Approach.Arch - Right at the base of the large stone arch in the Dynamo Approach. Very easy to see.
Dynamo.Approach.Cavern - In the ice cave on the way to the Alton Dynamo, above the door. You can jump up on the ice shelf right below and kind of float near the pyramid to open it, I didn't find a place to stand.
Dynamo.Deck.Dampener - In the very first room in the Alton Dynamo area.
Dynamo.Control.Door - In the first room with frozen Hive, just inside the first hallway door and to the left.
Dynamo.Observation.Valkyrie - In the open area with the reactor looking thing.
Dynamo.Observation.Core - In the small hallway just before the final room with the yellow bar wizard.
Dynamo.Core.Brace - In the room with the yellow bar Wizard.
Dynamo.Core.Brace - In the room with the yellow bar Wizard.
Dynamic.Core.Catwalk - In the middle of the large room with a bunch of pillars to the right of the first hallway. Hard to miss.
Dynamo.Network.Stairwell - In the same room as #6, just down the stairs left of that pyramid under the other stairs.
Dynamo.Server.Windshield - In the corner of the room with the pyramid in the center.
Dynamo.Coolant.Ventilation - This one is behind a vent that is located in the first room to the left with the Hive, same room as #2. Shoot the vent, crawl up on the piping below the vent to get in and it's right at the end of the ducting.
Futurescape.Transit.Service - On the right side of the ramp where you initially enter this region from the Glacial Drift.
Futurescape.Dock.Outpost - On the right side from where you initially enter this region, up the long ramp towards the building.
Futurescape.Dock.Garage - In between the two buildings south of where the Injection Rig spaws.
Futurescape.Dock.Silo - Just outside the Bray building, on the side Ana Bray is on, behind the large blue tanks (silos)
Futurescape.Reception.Overlook - In the Bray building across from Ana Bray
Futurescape.Plaza.Console - On the lower level of the Hive infested building to the left of the Bray building (there's a region chest immediately behind this one, under the stairs)
Futurescape.Plaza.Infestation - In the corner of the Hive infested building.
Futurescape.Termunis.Console - This is in the Core Terminus Lost Sector, in the room with a bunch of thrall and monitors on pillars - behind a pillar with a monitor. There is also a Clovis Bray system with information about Exo's in this room.
Fururescape.Ridgeline.Waterfall - On the right side of the path behind a waterfall on the way to the Dynamo Approach from the Futurescape.
Aurora.Mindlab.Observation - In the small room after the large octahedral (3D diamond, Warmind shape) there is a floor tile missing on the right side, fall down and look to the left.
Aurora.Mindlab.Supplies - Behind some crates (supplies) in the first area with Hive.
Mindlab.Conveyor.Junction - Just below the suspended Warsat in the dark room.
Mindlab.Conveyor.Bridge - This is under the bridge where the first Hive are inside the Mindlab.
Mindlab.Elevator.Right - Also in the Mindlab, down the right staircase in the area with the Hive Acolytes and Knight.
Mindlab.Elevator.Service - On the pathway to the left before you run up the tubing/wiring ramp in the first story mission.
Mindlab.Overhang.Node - On the right side of the area where you get the first Valkyrie in the first story mission.
X.X.X. - On the right side of the area just before you enter Rasputin's Mindlab.