Jer, it is pretty hard to have a warm-sounding receiver without a warm-sounding power amp section. Pre-amps tend to be more neutral than power amps. So, if you bypass the power amp section, it is a crap shoot as to what the tonal quality of the pre-amp section is. My bet is it would be more neutral than the receiver as a whole. Adding a bright-sounding power amp will probably result in an overall bright sound.
My recommendation is to get as neutral-sounding of a power amp as possible. You will probably own it longer than the receiver and a neutral amp will always be the easiest to integrate into another system.
My recommendation is to get as neutral-sounding of a power amp as possible. You will probably own it longer than the receiver and a neutral amp will always be the easiest to integrate into another system.