Poisonhzkj has rolled out an update to CXMB, a custom firmware plugin that allows users to load custom made XMB themes from the memory stick.
The update features compatibility with custom firmware 3.71 M33, however the author notes that you must use a 3.71 compatible theme.
Download CXMB v2.5
Custom XMB Plugin v2.5 (9/28) Update [2Alien]