I have one of these Pioneer Series 20 A-27's and I consider it the best amp in my collection!
I also have in my collection for comparison; Sansui AU-9500, AU-20000, AU-919, CA-F1/BA-F1, Pioneer Elite A-71, A-91D, Pioneer SA-9100, SA-9900, SPEC 1/SPEC 4 and several high end receivers from; Marantz, Mcintosh, Pioneer, Sansui and Yamaha.
I'm sure you recognize that all the equipment I have is highly regarded and represents quality at or near TOTL for their time but the Pioneer Series 20 A-27 stands above them all. The Pioneer Series 20 pieces will be the very last gear I sell if ever! Even the Series 20 tuner I have sounds better than my Sansui TU-X1! It is phenominal equipment that was built by Pioneer to make a statement and it does so with authority. I have done a lot of side-by-side listening in different rooms of my house with several pairs of speakers and the Series 20 gear always seems to come out on top!
As for the one on Agon, the asking price is high for the current market but I have seen them sell for more than $1K in the past. The unit on Agon is in very nice condition too which is not always the case with these. These amps are somewhat rare and only come up for sale 2-3 times per year. If it were a serious consideration for someone and you could get the price down a C-note or more I would recommend it highly. You couldn't get mine for any price. That's how much I like it!
(By the way I have NO affiliation with seller)