Well you are moving in the right direction with the RME. I would have that in my system any day.
My auto mechanic got a pair of two panel per side Magneplanars. I was in the process of trying to set him up with a pair of subwooofers for them.
I went over there one day and they were gone. He said he had burned them. (He is a very very impatient fellow under certain circumstances) It seems the adhesive failure had occured in these which were older. All I could say was "Ya shoon't have done that" but it was way too late.
I repeat I don't want my power amps adding to the sound. That is not what they are supposed to do.. If they need upgrading they were not designed correctly in the first place.
I have been testing my seventies vintage (UNRECAPPED!!) gear on a local test bench and much to my surprise it mostly tests as good as new. The young man with the bench is an engineering student who just got an Audio Precision Analyzer.
If you want to build yourself some amps and have already built some chasis and split power supplies go over to Neurochrome and buy some modules from Tom Christenson. They should be able to drop right in and utilize the heat sinks you have. I found out about his product line because of the line posted by the late great Sigfried Linkwitz, "I don't know how to measure such low distortion" He of course had a day job as a Hewlett Packard instrument engineer. Audio was just a slumming hobby for him.
I have two excellent vintage turntables but have not purchase a vinyl record since the 1980s.
Your mechanic was careless. Were those early 70s Timpani? First off, they don't need a subwoofer! You just don't take a 40 year old product and hammer it.. .and amps from the 70s don't sound so good compared with modern amps... sorry, but the best of them simply subtract but many of them, like the SAE solid state stuff, grates on my nerves.... use that Levinson Num 20 as an arc welder but not to drive music!
I just took my Marantz 2325 and Sansui G7500 for full rebuilds. Both have very low miles but the Marantz had a leaking cap in the power supply. The fellow has yet to open the Sansui.
I have a collection of 70s vintage but I only power up the ones that I have had recapped because after 40 years you can not trust the electrolitics.
Oh, I use the RME to record my LPs at 24/96. A Linn LP12 fully upgraded (OK, the Lingo is about 15 years old now).