I can't speak for the proac speakers, since I have heard neither. However I think the small stand mount plus sub combination can be very good for the smaller rooms, since it gives you much more flexibility in placing smaller speakers in the right place for imaging, and the subwoofer in the right place to load the room to create deep but not boomy or resonant bass. I use Spica angelus (a floorstander that sounds like a stand mount ... superb imaging and very thin bass) with a REL strata in a room that measures 10feetx12feet. I can get great imaging and great deep bass.
I also agree with other comments that perhaps the 2.5s would benefit from a good sub. Sure, I haven't heard the 2.5s, but it would take a mighty big main speaker to get into the 20 - 25 Hz region, and this region lends a lot of dynamics to the music, that I like, for orchestral and live blues recordings. I wouldn;t be surprised if most floorstanders wouldn't benefit from a sub, provided it was crossed low enough. RELs cross as low as 25 Hz, so you can partner with any speaker that does not go much below 35Hz, which is quite a lot of them.
AS I said I have no proac experience, but I am a sub convert ... I hope this info helps.
I also agree with other comments that perhaps the 2.5s would benefit from a good sub. Sure, I haven't heard the 2.5s, but it would take a mighty big main speaker to get into the 20 - 25 Hz region, and this region lends a lot of dynamics to the music, that I like, for orchestral and live blues recordings. I wouldn;t be surprised if most floorstanders wouldn't benefit from a sub, provided it was crossed low enough. RELs cross as low as 25 Hz, so you can partner with any speaker that does not go much below 35Hz, which is quite a lot of them.
AS I said I have no proac experience, but I am a sub convert ... I hope this info helps.