I know you have been a user of AVA products for many years now so we regret the SET 400 did not have the features you wanted.
I might suggest our brand new M225 mono amps we are finally able to ship right now after a long development period.
These are fully differential balanced designs with XLR inputs only. They are very small for their power and authority, just 9” wide, 10” deep, 4” high and 16 pounds.
They are Class A-B designs running Class A up to about 20W. The M225 is rated at 225W/Ch into 8 ohms, near double that into 4 ohms and safe operation into 2 ohms.
Sonically, they are probably the best we have ever done. We have review samples out to Parttimeaudiophile and Audiophila right now. The Audiophile reviewer called and purchased the review samples. Expect two over the top reviews soon. Huge stable image, amazingly natural, transparent, dynamic, and resolving.
Price $1699 each and worth a hell of a lot more.