. . . also, I am not familiar with the Bryston. Since ’01 I have been running a Cary V-12 amplifier (12 EL34s, a pair of 6922s, and a pair of EL84s as power source for the 6922s) which is switchable between triode and ultralinear. I almost always run it in 50 wpc pentode; I am thinking that perhaps this is not the most "tubey sounding" amp which may have an effect on how I perceive the SLP-05, except my perceptions of the SLP-90 ("sweeter and warmer") were also based on use with the V-12. Prior to the V-12 I had a pair of ARC VTM 120s (eight 6550s) behind the SLP-90, and in retrospect, that combination could take on a hot bombastic rocking sound that is probably what I would associate with sounding "tubey."
Back at least a couple of years ago, there was a member here who owns a SLP 98, and I distinctly remember him stating that his preamp was definitely a "sweet" sounding preamp. I’d say that might be another option for you to consider, except I don’t think the SLP-98 comes with any balanced ins or outs.
I know that Music Direct occasionally has Cary preamps and they have a money back audition period, as does Cary Direct--that is if you order it without any mods. That might be worth considering so you could judge for yourself how you actually felt about the sound.