John,
Congrads on joining the ProAc cult... you will forever have at least one pair. The 1s is a fine first treat. I have tried several subs on various tabbies and 1sc's and never was happy with results. It may have been the 14x26 (?) large room... but the subwoofer bass always seemed seperate. Gave up and bought Response 3.8's... giganormous improvement. But... kept 50 Signature's, 50's with 1sc mid/woofers, Tablette 2000's and couple other tabbies. If you have Smaller room where you spend a lot of time.. office, art room, bedroom, kitchen.. the 1s or other compact ProAc are purrrfect. But... as a girlfriend once said.. "Don't ask for what I am not able to give." Small speakers cannot convincingly reproduce a cathederal pipe organ.
With patience you could find pr of ProAc Response 2.5's for well under $2,000. They are smallish floorstanders that can provide a room filling top to bottom sound. Tube amps are really best with any of the older classic ProAc spkrs.. Stereo 70, 8b, MC240, etc. The only transistor amps that have the relaxed warm sound appropriate for extended ProAc listening are the 1970's Sansui xxx, AU and B series. Perhaps an acceptable step down would be cap coupled 22xx Marantz from same era. You will find your 1s spkrs respond to careful gear matching... and with any small spkrs, room placement cannot be overemphacized. It's all fun to mix and match .. and the weakest link will never be your ProAc's.