Can I replace the drive in the My DVR Expander with a larger drive and still maintain compatibility with the TivoHD?
No. The “My DVR Expander” enclosure has nothing to do with TiVo compatibility. The specific drive in that product is identified by the TivoHD software as compatible. You cannot replace the drive in the “My DVR Expander” with another drive and maintain compatibility with the TivoHD, because then you would be replacing the one thing that makes it compatible. Note the TiVo Series3 — but not the TivoHD or TivoHD XL– will work with just about any drive in any enclosure. Some drives and enclosures are more reliable than others. See Section IV for more information on unsupported solutions.