unsound - the Sonic Frontier (model unknown) preamp driving the Krell FPB 600 is what I heard when auditioning the final prototype of the 2.7 compared with the reference 3.7 in Thiel's listening room on my 2012 visit to Lexington. I have personally never heard better, although I must admit I've never heard any ultra high priced offerings.
Jim required amplification that he liked and that tested impeccably well. Those were his choices.