All very excellent questions
First...
I have an XS which has been in my system since I owned the X-1's several years ago.
Mine is an integrated 2 channel/multichannel and HT system.
I used the XS for music and hometheater only to find that with the X-1 and now the X-2 this is completely unnecessary.
I continue to use the XS with my HT for LFE
As for the MAXX ll...if it is purely for music, and, depending on the type of music you like, as well as how loud you play, in all hionesty the MAXX ll is a magnificent speaker for the money. It is a close call for me to say that the X-1 is superior except to say that it throws a larger soundstage. In our audio club I have the X-2, and other members have the X-1 series lll and MAXX ll. The member with the MAXX ll does use the WOWW sub and his sytem is superb. The member with the X-1 has 2 Watchdogs as well as an XS and his sytem seems less defined than the MAXX ll.
It is all what you are after and how you want to use your subwoofer. As I stated, my XS is now only for LFE in my HT. I think if you went with the X-1, there are great deals to be had now as well as a Series 5 upgrade that brings it very close to the X-2. If you are using it for music only as I have stated, I did not use a sub in my system.