My 30SE was bettered by the ARC LS 25 MKII in dynamics and detail, for what this info is worth.
I'll add to this thread the the 31 and 31se are SIGNIFICANTLY better than the 30SE. Ditto for the 50 vs 51SE. BAT is one of the better high end companies. You won't be making a mistake buying from them. Tom has the best advice, if you can try at home, do it. Just be prepared not to return it :).
The 31SE is a little more extended, more dynamic, better stage, better details. The 31 is a little sweeter and warmer depending on what 6922 tubes you use.
So glad you are enjoying music with the 51se and 75se. You know I have had my 150se mono blocks for almost 4 years now and I'm still in heaven with them. I've been getting out to hear a lot of systems lately and their is nothing I would trade my BAT pre and amp for. They have surpassed the performance of everything I've put them up against by a large margin in my opinion.