Low and High Voltage CAN go in the Same Box

All our lights are low-voltage.  I looked for boxes for the switches, but I was surprised to find the plastic LV boxes were expensive, and in my view, not that great.  I searched for a steel box and found one!  It is the Hubble product pictured below, the price is reasonable, (less than the LV mud-ring boxes) and the divider is removable (additional $1 for the divider), so the box can accommodate both regular household voltage and low voltage in the same double-gang box.  We used double-gang boxes for all our switches and plugs in the house - (almost all).  Most will have a CAT6 cable and an 18g. cable in the LV side, plus whatever goes on in the household current side.  From these, we can eliminate power adapters in the house by providing LV direct from the plug, and we also can use any 12V devices, and have DC lamps (so DC power direct to LED COB lamps).  DC-DC boost or buck pucks are available online now for about $5, so you can get almost any voltage you want by placing it in the box (we are supplying 28V), and it would remain within the electrical code rules as long the voltage remains below class 2 wiring limits.  In addition, every plug location becomes a data/voice/LV/automation/sensing/instrumentation node as well, without adding additional boxes all over the place.  So we can have things like motion sensing that controls things far away from the box, microphones, speakers, bluetooth, wifi, fire sensing, temperature, humidity, etc.

In many of the switch locations, there is no household current component, so the whole 2-gang box is for LV.

There are virtually no octagonal boxes in our project - Just one, actually in the utility room because I wanted to have a different source of lighting while the LV lighting system was being worked on.

You can see the LV wires come from above the plywood - they were incorporated into the acoustic floor assy above.  This could be done with 115V also, but you would likely need for it to be in conduit depending on the acoustic floor thickness.