Here's a summary of what I know about Tivo<->Xbox as it currently stands.
The current builds of XBMC will not work with the current stock builds of ccxstream and the stock versions of TivoX (where stock means versions that I haven't modified as noted below).
All versions of ccxstream should work with XMBC if you browse to the tivo manual (usually via My Videos).
To get TivoX working you can:
1) Use an older version of XBMC, with stock ccxstream and stock TivoX. I believe they builds stop working sometime in late December 2004.
2) Build your own personal version of XBMC from source after you have applied a patch which is available in this post or at sourceforge. If you apply this source code patch and recompile XBMC, the stock versions of ccxstream and TivoX will work (modified ccxstream and TivoX will also work but wouldn't be needed). This patch hasn't been neither accepted nor rejected by the XMBC team.
3) Use a modified version of ccxstream and modified TivoX. These versions avoid the need for a patched XMBC (so you can use any release of XBMC), but have their own set of issues as reference in the post linked below.
Stock TivoX versions are available at fatattitude, ozTivo, in this post and in a couple of other posts.
Stock versions of ccxstream available at fatattitude , in the All-In-One S2 and a couple more in other posts.
This post has modified versions of ccxstream that are built with the newer mfs libs. The modified versions of TivoX that go with these ccxstreams are here
Note: xboxtv6.itcl is required by TivoX. It is how TivoX interacts with the Tivo (except for streaming shows, in which XMBC goes through ccxstream).