HDSP now supports analog audio and SDI video (on a very basic level)
For synchronised recording you need to use an external timecode generator, feed the timecode into both your HDSPs, now when you record both decks will have matched timecode and your recordings will be in sync.
Hitting the play button on both decks at the "same" time isn't very accurate - it is much better to use an external VTR controller. You can find an old deck controller for peanuts, eBay always has a selection of suitable devices. The protocol has remained the same for decades so even really old controllers from the early 90s work with the hyperdecks.
http://www.videotoolshed.com/?page=products&pID=42 is able to batch process timecode changes.
cheers
tom