Amp choices

Merrill Audio Veritas mono blocks will rock the 3's. These amps are refined,musical and will let the SF3's come alive in a way that is very involving and natural. The SF's need power to sound their best and the Merrill's will deliver in spades.

It sounds like a Pass 250.8 is something to look at as a real serious upgrade.  You are correct that the A21 is probably better balanced, but the 8008 has more control of the speakers.  I'm using AZ Hologram ii speaker cables and Wow ii interconnects.  I could probably do better on the interconnects maybe with Matrix ii or something from AQ.     

I would recommend a pbn audio amplifier 

I know this discussion is mostly two channel purists! Presently driving pair of psb imagine t3s with krell foundation 4K and halo A51 parasound amp! Wired wth Cardas clear reflection cables! Parasound amp seems to stage and image psb t3s well! Feeding krell processor with ps audio DSD and PWT pairing ! Sound on given recordings life like! A21 amp I'm sure may be similar! Just my opinion !