The A60 will drive just about anything you care to put on the end of it, just not to party levels. We know it can manage Isobariks 'cos they once did a show using them. Saras might be questionable. I don't think it's thin on the bass. It may not have the world's greatest grip and slam but it goes deep enough.
If you can find out if it will do Saras, that would be my choice - and you'll get a little bit of extra volume. Ultimately the AR18s and the MS10s aren't really that great a speaker, though they were fantastic for the £100 or £120 you paid for them. Slightly depending on what you listen to, another speaker that I'd suggest is the old KEF 104. It's a bit big but it's surprising good with a T27, B200 and a B139 passive radiator. Very easy to get along with and it will be dirt cheap. For more volume still the newer 104s could be a possibility. They have a ruler flat impedance curve, so no problems on driving, and I would guess are also a bargain these days. (£107 for 104s and £285 for a rosewood pair of 104.2s on ePay completed listings).