Maybe just maybe you're really asking about a Balanced Audo Tech preamp? vs the flying lil rodent?
If so, it's usually associated with a robust, deeply engaging midrange. Still great highs and lows, but this robust midrange is a character rarely heard in other brands.
I used to own a BAT pre and amps. My opinion, in this particular area, they are state of the art.
Hope this helps...it's worth a listen, great stuff !