You have to remember that the crossmember is intended for a V8 car with headers so you are going to run into some interference issues. As far as the downpipe not being up to standard - if I was the company in question and knowing the attention this build is getting I would be sending you a new one and PAYING to have my POS returned to me; along with issuing you an apology.
As far as the gauges go... who cares? You won't be able to read and process the information fast enough for their accuracy to matter. Your best bet is to tie in some pressure transducers into the oil and fuel system, plug them into a PowerLogger and call it a day. The best you get with gauges is that something went wrong, datalogging can at least show you trends leading up to potential failure.
It works for a V8 but also for a turbo car, the cat back slides through there perfectly so it wouldn't line up even if the crossmember wasnt there, so its off no matter what. Honestly its just faster to fix it then ship it back and have one sent to me again.
Gauges are purely for appearance reasons for me. The scanmaster and an aftermarket boost and fuel pressure gauge would have been fine. I'm not trying to push the car anywhere near its limits or squeeze an extra 10th out so hopefully no catastrophic failures in my future to watch out for.