No probs.... well... they've gone about it a little backwards and I think in reflection they might do it differently.. in fact, I KNOW they are because they are getting a RED scarlet next year which will give you 3K resolution and let you use your own lenses... see here, http://www.red.com/epic_scarlet/, for top shelf techno action! It's modular so you still have to configure it to your needs. Hard drives, lenses adapters and lenses etc etc... but it's niicccceeeee! And will probably work out as being the same price as say a Sony EX3 which would be an equivalent I guess.
As for the HV20. Well what they've done is for starters, they use a Beachtek, http://www.beachtek.com/dxa6vu.html, to get XLR shotguns in to the 3.5mm mic input. Be warned, the Beachtek website will rave on with Ray Vaughan at you.
That covers the sound. They then connect the HDMI output with a blackmagic HDMI to SDI convertor, something from this range, http://www.blackmagic-design.com/products/miniconverters/techspecs/.
That enables you to run SDI cable as long as you like with naff all deterioration of the signal and minimal interference. They did try using a HDMI to CAT 5 converter as you can run CAT 5 cable for considerably longer than HDMI, but SDI is a lot more robust than HDMI. We were shooting on a beach using a generator to power everything and that gave us all kinds ground loops and interference in the audio when we didn't have the beachtek which has a ground lift on it.
The SDI out then goes in to a blackmagic video card. Something like this, http://www.blackmagic-design.com/products/hd/.
They use a, carrroooggghhh tttt.... PC to record the footage and they use Cineform codecs but really, capturing with Apple ProRes would be just as good so you could do it in FCP still.
The other trick bit of kit they have is a Brevis lense adapter, something like this, http://www.dv.com/reviews/reviews_item.php?articleId=196604148.
It enables you to put SLR lenses on so you can a) use nice lenses but b) have a lot more control with your f stops and will even enable decent focus pulls including focus marking when you put something like this on, http://www.dv.com/dv/magazine/2007/October/focus1007_1.jpg.
The other thing that became quite important was being able to frame things properly as the image that was coming out of the HDMI was nothing really at all like was seen on the viewfinder/ LCD. So they use a spare SDI output from the HDMI to SDI convertor to feed a 7" panasonic reference monitor. which is stuck to the overall rig... which as is pretty big at this point. So you need a good tripod to take the weight.
They went this route to begin with because it was done on a budget but as things progressed, they wanted to get better and better results from it so in hindsight, I would say if you are starting of with a HV20 and you want to add to it, then this above will get you good results. However, if you are buying everything from new/ scratch, I'd probably advise a much simpler rig such as the RED scarlet because would you believe, that thing only costs 2 and a half USD!?