Xenosaga 1 is a dual layer game and won't work unless you split it, but you probably already knew that. There are threads about splitting it in the DVD rip forum, so that is a good place to start. I have an echelon release that is single disk with compressed videos and works fine with SM2. It was a lot simpler in this instance to just D/L another copy than to backup my original. As for Xenosaga 2, try zoneloader or cd loader (which can be found in the swap-chat forum) and check swapmagicfix.com and see if there are instructions there.
I tried Zoneloader and to my surprise, it did work with Xenosaga II. Even better was the fact it booted the originals. For the copies of XSII, Disc 1 needs TOC swap on SM CD 3.0 while Zoneloader boots disc 2.
XSI however has been split, burnt, patched and burnt again and to no avail. It just doesnt want to work. You know where I could get instructions on making XSI DVD5? I have searched before, no luck.