I would stay clear of the Maxx, I've heard plenty of horror stories, that's why ADJ doesn't distribute it anymore (It's still produced in Germany), but thay still distribute the Mighty Scan.
The XP3 is unbeatable for the money. Yes, the Auto Spot 150 is better, but it costs more. Definately go for it IF you can afford it, but I'm assuming that if you are looking at XP-3s, you can't. Maybe it would be a good idea to get 2 more Mighty Scans and 2 XP3s to put on top of the speakers?
By the way, you could use the "Search" feature at the top of all of the pages and search for "XP3". I found 47 threads, there may be more info in any those.
ALSO...Welcome to the forum