Downgrade to MW5, How?

[TMB_XV6700]

Nehemoth,
All the usual rules apply regarding USB connection and latest activesync installed, etc. (My understanding is although activesync isn't directly involved in the flash process, you still need activesync's usb drivers to communicate with the phone.)
Generally, you just download and run the file and follow the directions provided. IIRC, the updater will want to start from your phone being in the cradle, just sync'd - then the program will talk to the phone, put the phone in bootloader mode, show you some windows, and flash the roms (nk, ms, radio). Bootloader or CID issues may cause the process to error-out or get stuck somewhere, but the workarounds depend on the details of the problems, if any. As far as I can tell, so far, you've said nothing that implies you will have a problem with these steps. Downgrade away.
[I personally don't think you're sync problems w/ WM6 are insurmountable, but since your phone history seems a little cloudy, running this update followed by a hard reset or two is probably a good start to correcting your problems.]