I went ahead and had the Choke upgrade to my 7B SST's done at the Bryston US Service Center in Vermont, and am very pleased with the result. Not only does the top end seem much silkier, but the mids seem more dynamic as well (this is thru Merlin VSM MME speakers and a Joule LAP 150 MK II preamp). I swap amps back and forth between the Bryston 7B SSTs and Joule VZN-100 MK III Marquis OTL amps, generally acknowledged to be the ultimate amp of any type, tube or solid state, for Merlins, and the Bryston 7B SST "C" series amps come very very close now. not quite as "real" in the midrange as the Joule OTLs (nothing is) but with perhaps a bit better low end. The C mod turnaround was one week door to door and Bryston even returned the amps in new shipping boxes. Highly recommended!