Well then I echo the question above, what changed to now make you feel its bright? Realistically I have had audioquest designs back in the 90's
they were always a bit Grainy and harsh with some components, mostly due to the multiple solid conductor litz type arrays the speaker cables seemed to use. At the time Kimber and Audioquest along with monster and MIT, straightwire, wireworld were mostly available at most of the higher end home theater stores when they started all changing over from 2 channel to multi channel focus
However again not sure cables will completely solve the problem, it seems more like a room and or synergy of the components issue, and if in fact the Plinius you list above is a standalone amp than what is the preamp used? This will have a bigger effect in many systems tonal balance than the amp. Or are you just running the bel canto straight into the amp with its onboard volume control or something? If so that is your issue, you will need a full frequency preamp to add body back to your digital sound helping eliminate the "Digititus" that many experience running direct eliminating a good preamp. Has more to do with impedance and just harmonic problems that make music lose that full organic feel.
However again not sure cables will completely solve the problem, it seems more like a room and or synergy of the components issue, and if in fact the Plinius you list above is a standalone amp than what is the preamp used? This will have a bigger effect in many systems tonal balance than the amp. Or are you just running the bel canto straight into the amp with its onboard volume control or something? If so that is your issue, you will need a full frequency preamp to add body back to your digital sound helping eliminate the "Digititus" that many experience running direct eliminating a good preamp. Has more to do with impedance and just harmonic problems that make music lose that full organic feel.