I'm sorry I thought it was 1 522 duo for 2 508 solos. So you are going from 2 Duos to 2 Solos. That's alright if you do not need the extra recorders and their disk space and have no extra TVs. You could return the 522s and get a one 722, so you would have more disk space and HD if it comes to you and be "modern" for only $3 more. But if they need to be in widely spaced locations then more thought is needed. Remember the RF signal out of the 722 is as good as the composite and maybe even the S-video from 508s.
-Ken