Can anyone explain any known differences between these two series of amps? I ordered a 5503 (200 wpc x 3) today to compliment my older 555 (200 wpc x 2), but then noticed that the new 7700 (175 wpc x 5) is the same list price. If there's really no performance differences (25 watts is in no way a deciding factor for me) I think it's a lot easier to have one chassis instead of two. Also, audio racks get limited when you've got to have a middle shelf that can hold at least 60 lbs. At least w/ the one heavy amp you can throw it on the bottom shelf no problem. Please help fast, they told me a couple of weeks until the new amp arrives, but I'd like to call them tomorrow.