Hmm. The claimed sensitivity, bass extension, and not exactly huge cabinets seem to violate Hoffman's Iron Law. If it's a bit of marketing-optimized specsmanship, a la DefTech or Klipsch, it's worth considering when pondering the amp question. So let's do that. If they're only 91 db/w/m, using your Rotel's available 120 watts(8 ohms), that would still be approx 104db (peak) at your chair. If, say, the sensitivity is wildly overrated and they're only 88 db/w/m, 120 watts is still 101db.
Also, their impedance is spec'd as "4-8" ohms, but let's just go with 4 ohms as it's the most demanding, worst case scenario. Your Rotel can do over 200 watts into 4 ohms all channels driven, and 264 watts driving just two channels, per measurements done by Sound&Vision. So for three channels, as you are using it, probably allows well over 200 watts. That should be enough for reference or near reference level output, even if the speakers are less sensitive than advertised.
So, yeah, unless you're some sort of masochistic headbanger who constantly cranks it to eleven, you probably don't need to worry about it.
Room looks very nice, as do the speakers, and the new sub will be a significant upgrade.