I own 4 of these Mattes SSP-200 amps! Back when Mattes Electronics was in full swing, I bought their integrated version and loved the preamp. At that time Mattes blew away everything on the market, and McIntosh hated Mattes, so much that if any Mattes showed up at their testing clinics, the techs were told to blow the fuse, so it couldn't be tested. My integrated was very unique, in that it put out 120 RMS per channel, because I took it to the factory in Chicago on a Saturday and the Manager Tech did some modification changes to mine to bump it up 20 RMS more per channel!
I am now 68 years old and became an extreme audio enthusiast in my early 20's. When I discovered the Mattes sound I went banannas, there is nothing like it even to today! Back then I used Altec speakers with the 811 horn and 2-15" woofers in each cabinet, (bass reflex, very high SPL), I eventually bought 2 more of the same Altec's, and wired the woofers to add a doubleing factor. The extreme power and unbelievable low distortion, blew everyone away, with no fatigue after hours of high level listening. I was into rock music back then and the Mattes was the only amp that could 100% deliver the full dimension of sound on recordings like Led Zepplin's Dazed & Confused, and Edger Winters Transulvania. I bought all of my 4 Mattes amps on Ebay from people who had no idea what this exactly was in grandpa's closet.
Of course there's always a down side, being I'm retired in Phuket Thailand now, and can't presently find a knowledgable tech to work on 2 of them. I tried many times to get a sam on line, but only wound up with a very faded copy for $20. Power surges are common in Thailand, so I use a CPU to try and protect my baby, some what.