Did you consider the TSN-PZ adapter (+ Canon EOS T-adapter) to connect your XTi to the scope? Here's a page with pictures from an 884 with an XTi and good descriptions of the shooting process.I already have the Canon digital rebel xti, but there is no 2x
teleconverter, or even 1.4x that works with this camera in AF mode.
http://www.digital-nature-photography.com/nature/info/digiscoping-kowa-tsn-884.php
The two adapters should be less than $500.