There was a review of the 5 se in Stereophile a couple years ago as an addendum to the 50se review I believe.
The 5se retains some of the warmth of the 5i while sounding more dynamic, less "tubey" and habving better bass definition. I've only heard the 50se briefly, but it sounded fast and clean, more like a solid state unit to my ears.
All BAT gear needs time to warm up at least 1/2 hr if well-broken in. New gear needs break in time, so if you're auditioning, keep that in mind.
