I have a space in my home theater cabinet to fill
Listen, Adam. Here's the simple answer: An XPA-7 will be great to fill your cabinet with a home theater component. It will work fine with what you have.
Don't misunderstand all the replies. We're just saying that you'll actually HEAR more improvement with a sub than an amp. BUT, at some point, an amp is likely in your future just because every really cool home theater needs an amp. Right?
So if you want to fill your cabinet, get the amp and put everything back together. When you get more money, spend it on subs. If you really want to minimize disturbance to your cabinet, go ahead and get a 2nd sub cable and plug it into SW2 on your AVR before you put the cabinet back. (Get the right length cable.) Then when you add a 2nd sub, you'll already have the cable plugged in.