I have an Omex ECU and the Ph1 throttle conversion. I also still have the standard ECU because it's controlling some other functions of the car - not sure what.
Anyway, my advice is don't do it. The cable operated throttle is the only thing that lets my car down. It's very jerky and has a tendency to stick quite a lot, which means a 2,000rpm idle sometimes, worse fuel economy and a heavier throttle pedal.
I'm not trying to sound like a fan boy, but K-Tec's Gen90 ECU can run the FBW throttle and can do everything the Omex does plus more. It'll also make your dash work properly (well, eventually...).
Personally, I'm going to ditch the Ph1 throttle arrangement and go over to this setup instead. No amount of trying to fix the sticky throttle issue has made any difference and I doubt the throttle response would be any worse than it already is. It shouldn't cost too much either, since my loom hasn't been modified in any way, and looking at the price of the Gen90 compared to how much Omex 600's are going for on eBay, I wouldn't be more than a couple of hundred quid worse off.