Sure, from your comment that the 6 15/16" 607 barely fits and the 7 5/8" 906 doesn't, even with feet removed, it appears that you're working with about 7". If you could remove a section of shelving to possibly double the available room this would help. You could then consider the 876 or another 906.
Since you already have a 607, you could do some experimenting so that we wouldn't be doing just guesswork. Temporarily set up the 607 with speakers down there and see if the setup would play at your listening level without overheating and shutting down.
