How do I combine UltraArc and CIUv2?

[KaktoR]

You got it. XTool inflates files.

after this, you should always use srep+final compressor (lzma(2), lolz, rz, ...)

Output will be smaller in 99% of cases then if you don't use xtool (which is a precompressor btw).

But it has all to do of which streams a file use. Some games didn't have a compression at all and in this cases without xtool should be the best.