A4 b8 b&o sub upgrade - amp signal help


Registered User
Hi looking for some wiring help. Going to install a hidden box with a Rockford fosgate dual 2 ohm sub with a vibe micro mono amp into my b8 avant with b and o, factory subways missing due to air ride components in the spare wheel well. The main Issue so far has been finding space, after removing the amp, tuner and nav dvd rack, and finding space for all the units along with the box and amp in the same space, but think I’ve managed now!!

My two questions are about inputs to the amp.
1) should I use a line output converter or just use the amps high level inputs? Read cases for each, but unsure if the factory sub high level will get a limited signal because of the factory crossover or not? And if I use a loc, will I loose the mmi control over bass levels as compared to speaker level inputs?

2) About running a mono amp and sub. Is it better to use front speaker wires (full range I think) or the existing sub plug as the input for either loc or high level in the amp? Again will the mmi let me control bass levels through the aftermarket amp by adjusting it on screen if I choose the sub plug as my input?