I almost when down the PAS road. I looked at all of the various upgrade boards out there because I didn't want a stock PAS, I wanted great performance. Ultimately I was able to build Roy's SP13 for around the same cost.
Within seconds of playing music through the SP13 I heard way more detail with a bigger soundstage and knew I made the right choice. Changing the output caps the Clarity CMR and a couple of the power supply caps to Clarity TC upped the resolution a few more notches. I saved a little money building it into a relatively cheap aluminum Hammond box.
What Corndog has said is so true .. I played around with PAS preamps for 40+ years. No matter what you do with them > bypass the tone controls, beef up the power supply, alter the RIAA curve etc., etc., they will never sound as good a one of Roy's SP preamps.
Those who read this board know that I love older Dynaco tube gear. The PAS preamps are nice to have if you are a collector of vintage tube gear but in stock form or even if modded, they are not the best sounding preamps to use with any amp. The Dynaco PAS preamps always held back the Dynaco tube amps from performing their best.
Here is a true story .. In the late 1970's I was still cruising along with my Dynaco PAS-3 preamp and ST-70 amp. A friend (Paul H.) lived diagonally across the street from me and had just bought a solid state preamp from a company in Oregon called Audionics. He asked me if I would like to try it out with my ST-70. The next day he brought it over, I hooked it up and we listened. From the first minute, I could tell that this preamp had much more "jump factor" on transients then the PAS preamp that I had. Things like bass drums, cymbals etc. really jumped out at you. The PAS3 sounded "muted" on the same music on every transient spike.
Just my opinion but if you are looking for the best sound from your music system, you shouldn't really consider any of the PAS preamps as your front end ..