Since you're using a 7-channel (with 5 powered channels) AV receiver and have a subwoofer, is this a surround HT system or are you using it for 2.1 ch. stereo?
I notice you're considering changing to a 2-channel integrated (Anthem 225), so I'm guessing you're not using the Rotel for surround sound. I just looked at a photo of the back panel of your sub and you really don't have to worry about whether you can hook it up with whatever you buy. Your sub has a versatile set of inputs--you can plug in a mono LFE RCA interconnect, R-L stereo interconnects, or speaker cables. The Anthem 225 has a pair of preamp-out jacks, so you could use a stereo pair of interconnects to drive your subwoofer. If you were to get a stereo integrated amp *without* pre-outs, you could still connect your sub with speaker cables.
Now on to the speakers. I have recently auditioned a pair of speakers that should be about perfect for your situation. 20x24 is a large room, and many good floorstanders that can fill that space are above your budget. However, the Monitor Audio Silver RX8 is an excellent, well made speaker with a neutral tonal balance, excellent low level detail, and BIG sounding in a modest size and right about at your budget. They retail at $1750/pair (here's a demo pair
right at your budget) and are a demure 38" high. I heard these in a ~16x20 room and they were actually a bit much for it. They should be perfect for 20x24. In fact, this double-ported speaker comes with a pair of foam plugs for the ports if you need to dampen the port output to fit the room. That gives you 4 different physical bass damping configurations.
I also listened to the next size down, the RX6, which is slightly smaller and has one less woofer. It's amazing how much more sound Monitor Audio got out of the RX8 with just one more woofer. The RX8 makes the RX6 sound like a compact by comparison--nice sounding in the sweet spot, but not at all room-filling like the RX8. The Absolute Sound noticed the same things about the RX8's clarity, detail, smoothness, tonal balance, dynamics, and room-filling abilities in this review
. It was also a TAS Editor's Choice.