There's an entire forum dedicated to the HR20 over at dbstalk.com. Earl Bonovich seems to be the "champion" for the HR20 and has a very detailed review of the DVR posted in a sticky with lots of photos inside and out. You may be able to identify some of the major chips from the photos but I haven't looked at them in a while and don't recall how good the resolution is of the photos.
There have been quite a few posts indicating that swapping out the original SATA drive with a different one (i.e. larger) works quite easily IIRC. I don't remember if using a larger drive actually gives you the expected increase in capacity or if it indicates the original size similar to restoring an image to a Tivo without expanding it. I do know that the external SATA ports have been enabled via a recent software update but I believe the OTA tuners are still inactive.
Please don't PM me or any other members looking for personal assistance. You'll do better by posting (after you've exhausted the search feature, of course) and taking advantage of the collective expertise of the membership instead of a single individual that may or may not be able to help you. Thank you and enjoy your stay at DDB!