Activesync will not connect from the bootloader. This is not a problem. Activesync is not needed to flash your phone. You just need the USB connection in the bootloader. As long as you see the letters USB in the corner you can flash.
Did you use the shelltool in the attempt to load the other WM6 rom? And if ActiveSync is required to use the shelltool then you may have to flash an official carrier rom in your current state (one that matches your CID so it will flash) and once your device boots again you should be able to use the shelltool and load the other rom that you want.
Personally this sounds like a big hassle to me and if it were me I would just pay the 25 bucks or whatever it is to get the unlocking software from the unlocker website and CID unlock my device so I could pretty much flash at will (G4 safe roms of course)
Rom: Shogunmark Death v4.1
SuperCID with Pof unlocker V3
Rom: vp3G's v3.61 -- fat to phat rom