The ProAc Response 1SC's are one of my favourite speakers - I think in this case they just need something a bit better than the 8xpd. Either that or it just wasn't a good match in this case. I think what you're after is a larger speaker, so take a look at speakers like the ProAc Response D2, ATC SCM19, KEF XQ20, and Monitor Audio GS10. All these use larger bass drivers than the 1SC (now replaced by the D1), so will be more capable when things get busy, and should give you a bigger soundstage as they'll hold less back. I would still rate the Response 1SC's up with any of the speakers I've mentioned above, they'll just lose out a little in bass response and power.
All of those I've mentioned, other than the GS10's, will work fine against a wall.