The MTS - which I've owned (and loved for HT/music dubties, BTW)- have a little bit of a foreward presentation, are very clear, uncolored sounding, lots of detail, and very good dynamics. They are still about 6ohm load across, dipping even further. You do have the advantage of some EQ on the subs (do you have the sub modules?), which will help greatly, yes. You may or may not need any other EQ, depending on your room, setup, and acoustics.
If you can get very good smooth results with your speakers alone, in your space, you have options, as far as receivers go. Those speakers deserve the best electronics possible, as long as it complements the speakers (i.e, tonality, current delivery, etc).
All that said, do you need/want the latest codec's, HD, HDMI switching, EQ, etc? If not, used market has Arcam receivers, older Denon flagship's, Integra's are descent, and maybe a B&K, or even a NAD or Outlaw piece, potentially - which should all tonally compliment your MTs', by adding a more relaxed, warmth to the sound, still give good current delivery, etc.
HK's are good for their money, no doubt. Modified, they're even better I've heard. Still, if I went with something like the AVR354, I'd, yes, have em tweaked, and add an outboard amp likely for more "umph". But, they're strong current pieces, so maybe it would be just fine for ya. Dunno.
I would consider separates first, and more costly pieces with your speakers, ideally. Your speakers do potentially want the best you can give em, as I said.
Would I personally stay with a receiver with those speakers? Um, no. But then I know what good separates can do. I'd be looking at the more expensive pieces at a bargain price, with the sound quality and bells-whistles I need. But, the speakers are the most important part of the chain, sonically. So, you might just get some superb sound if you chose right on the AV receiver front.
