The first post on this sticky thread has everything you need to know about upgrading your TiVo HD. (Section III, #30 covers internal upgrades.) Are you you interested in upgrading the internal hard drive in your TiVo HD? As mentioned, that's the way to go rather than adding an external drive. If you don't need to save your existing recordings and you're using winMFS you don't need to connect both drives at the same time. You'd connect your OEM drive to the PC to copy the OS image then you would connect the new drive to the PC, copy the image to it and do a couple of more steps to finish the upgrade. That will save all of your cable card settings, season passes, etc., just not any existing recordings. Put the new drive back in TiVo and the OEM hard drive on the shelf as a backup and you're all done. Yes, you could use an Antec MX-1 case, but you don't need to. You could simply use a USB/SATA Adapter like this one and save some money. Unless of course you need an external enclosure for some reason in which case the MX-1 is a very good choice. (I'm using one w/1TB drive for Time Machine on my iMac). If you want to save your current recordings you could try connecting both drives at the same time to copy everything over, but via USB it could take a long time. A better bet is to transfer the recordings to your Mac using TiVo Desktop and then back to TiVo after the upgrade. winMFS is quite easy to use. Just follow the directions on the first post or on the MFSLive web site and let us know if you have any more questions. Happy upgrading!