Just happened to notice your topic.
I am a long time ProAc advocate. I currently own an older Response 2.5, and I'm very satisfied with it. While on my audio quest to build the best system possible within my means, I owned and auditioned at least 50 pairs of speakers. I made most of my purchases on A'gon buying low and selling high, which enabled me to enjoy as many speakers as I wanted. My quest ended about a year ago, and now I just enjoy listening to music, and don't have much interest in changing components these days. I've actually scaled back quite a bit from components I used to own.
I purchased at least a half dozen ProAc's, and liked them all, except ironically the most expensive pair - the 3.8. For a stand mounted speaker, the Response 1SC was my favorite, followed closely by the Tablette Signature. A real benefit of ProAc is they really hold their value. The 10 year old 1SC still goes for about $1200 on A'gon, and the 10 year old Response 2.5 generally goes anywhere between 2,000 and 2,500 depending on condition. I prefer the sound of the older ProAc's to the newer, but that's just a matter of personal taste.
All ProAc's have excellent bass when you consider the size of the drivers. The drivers are some of the best out there using ScanSpeak midbass and Vifa tweeters. I believe a big reason why they are so musical and enjoyed by so many folks is their use of just 2 drivers and a very simple first order crossover. Their method of vibration control is also simple but extremely effective.
They do seem to be a very good match for tube amplification. It might be due to their benign impedance load. I have mine mated with an Audio Research VT200, and a tubed SAS Audio Labs 10b preamp.
Having said all that, I still think the Dynaudio Special 25 was the best speaker I've ever owned, and I'm very interested in the new Focus 140. I'm hoping to audition it soon. At $1800, it may be one terrific bargain.
Let us know how your search turns out.