I2S amp might be pretty cool, and might give better sound quality. 2-cell battery packs really only makes
sense if you have a constant-current power supply I think, otherwise you're just going to waste a lot of power in resistors.
There are a few, LED2001
(Quad channel, VIN=2.8-16v), or even multiple AMC7135. The first two will require inductors. I want to find some 1A constant current ones like the AMC7135 that can handle the 3W LEDs with no resistors required at all that will also reduce component count on the PCB.
[on the ESP32] That would be pretty cool. Are you intending to build on the TeensySaber code base? I might be able to help out with some of the software stuff if the thing you're interested.
I was thinking about it or looking through the other code bases(LightsaberOS,FX-SaberOS). I like your pick of IMU better than the MPU6050.
I've been thinking of replacing the booster with another chip that automatically switches between buck and boost and can handle inputs up to 16 volts, which would be kind of cool as anything up to 4 cells would just work. However, as I said before; without a constant-current drive system, dual-battery setups aren't that great.
Well if you do go down that route later look at the LTC3114
or look at this ULDO 3A LP3963
set to 3.3v. The I2S amp I was looking at is the MAX98357A