For reference, my own system has been running about 6 months - total of about 60A max draw, most channels driven at minimum acceptable impedance, and the impact to range has been below measurable levels. No visible impact to 12v accessory systems either (no lights dimming, etc). It's been so surprisingly low impact that I'm planning to ~double it
the one thing I've been extremely dissatisfied with is the head - I thought due to its interaction with the rest of the vehicle I'd figure out some way to make line output converters work, but it just hasn't been an acceptable solution. The output from the head unit itself is simply too low quality.
If giving up some functionality is acceptable, you can definitely run an aftermarket unit, but you lose quite a bit:
-Control over charging timers
-Display of climate control functions
-Remote control (climate/charging) functionality
-All carwings functions
-Setting of car functions like auto headlights and auto door locks
-most power consumption/usage displays
Now none of those are functionally critical, but some are relatively important - probably most notably being the charging timer controls.
I started development of a USB device and PC software to interface via CAN and replicate a lot of those functions (so you could use an in-dash PC to replace the stock head unit), but got distracted on other projects. I did get basic CAN-to-device and device-to-PC functionality, but that's about as far as I got. Need to get back to work on that darnit...
Most of the development is just needed work, no hurdles other than time... The only real hurdles I had were hardware... I really don't want to cut wires, but I need to interface with about 2/3 of the ridiculous number of wires connected to the thing
Wish I could find wired connectors to connect to all the plugs, but I'm pretty sure that's not happening. Thought about dissecting my stock unit and just using the plugs from it, but when I found out the factory prices them in the $1200 range, I thought maybe I should keep it intact