I'm trying to find the right speakers

Aperions and Rockets are ID so you are not going to find it anywhere else except buying directly from them. Check their respected site and ask for an audition. While av123 forum is still closed, you can find most members at tweak city audio forum. Request an audition.

Polk Monitor 70 is clearing out, might not be that easy to find them as well. Anyways, I won't even put Polk Monitor in the same class as Aperion or Rocket. Polk LSi but not their Monitor Series.

What is your budget? The speaker choices you came up are ALL OVER THE PLACE. How did you came up that these are your 3 choices? The RS1000 current price is at $2600 while the Polk Monitor 70 can be found for a few hundred dollars, if you can find them.

I would be wary with av123 ATM given their financial status and availability ups-and-downs.

Definitely look at the Salk thread for Song Towers. The standard one is under $2K, but you may end up spending a bit more for the ribbon tweeter... (I think it's $1700 and up -- depending on finish -- for the dome tweeter and $2400 and up for the ribbon.)

I normally do it the other way around. I would listen first to make sure that I like the SQ then ask for more info such as support, pricing, durability ......

For floorstanders around your price range, check out
these
and these
Imho, in terms of accuracy transparency and overall SQ the above would serve you better than the choices you listed.

I currently have a 2 pairs of Mirage AVS-200 in a 5.1 setup. I'm about to purchase a Denon AVR-2809CI and I'd like to get another pair of speakers to change to a 7.1 setup but the AVS-200 is no longer available anywhere. How do I best go about selecting an additional pair of speakers for this new setup?

Should I purchase a new pair of front speakers for L and R and relocate the existing to the back (Lb and Rb) or buy speakers for Lb and Rb?

The Denon AVR has Audyssey MultEQ XT so in theory it will compensate (at least somewhat) for major differences in the speakers....in theory

Any advise would be greatly appreciated.

I could never reccomend AV123 or the RS1000's either. I tried them in my system and the crossover in both speakers went out in less than 10 minutes. I Plugged the old paradigm monitor 11's back in and no problems. In short, I upgraded to Paradigm studio 100 V4s.

AV123 gave me a "partial" refund, even though they admittedly sent defective gear after weeks and weeks of headaches and 1/2 truths in emails and dodging phone calls.

All in all this experience was a blessing! The Studio 100's are amazing speakers, not weak, recessed, or veiled. They are extraordinarly punchy with excellent impact, clarity, and great low end. They match well with with an svs 13 ultra sub and xpa-5. In essence I can't say Im upset about being burned by AV123 as I TRULY ended up with a FAR superior speaker, reliability, and in my opinion, superior sound!...which is the most important to me. There are many reasons why people love Studio 100's. I say give them a listen. They are incredible! Used and floor model prices are in line. I picked up demo's of the 100's and cc690 center for a little over 2 grand in Pristine condition in rosenut. Check out Audiogon and vidiogon as well for the 4 series as the 5's are now out.

How large is the listening area? Aperion has 30 day in home trial and FREE shipping BOTH ways-depending on your room size maybe the 5 series would be better.