Steve, I am using the digital out of my Mac into an outboard DAC so itīs not possible to adjust the balance or loudness through the computer. I believe this is also true on a PC.
Took out the Audible Illusion preamp, precisely adjusted the volume levels for each channel, and the speakers sound great. Problem solved, but nice to know a simple attenuator can be used for a rough fix.
Incidentally, I have a pair of Decware Radial 1.5s in the back (balanced through a Lexicon processor) powered by a Decware Integrated amp. Also, a Decware subwoofer. In the bedroom, a Taboo amp. All your gear sounds great, so a big thanks is in order.