HTPC with OTA HD TV recording and itunes music playback

Staying in OS X, anything you have can handle iTunes music, even a single G4. If you want optical out to your AVR that means at least an Intel Mac Mini or Macbook. For recording and playing back OTA HD with the most common OS X recording software EyeTV, you'd need a fairly decent Core 2 Duo, no older than the 2.53 2009 Mini. Any Mini from 2010 to 2012 would do a great job for you in the home theater. An older C2D Mac can record, that doesn't take much effort and do a passable job playing back 1080i recordings, but if you're at all a critical viewer you'll see flaws with anything in the 1.83 to 2.2 C2D range.

An HD Homerun is a dual tuner that can do ATSC which EyeTV supports:

http://www.amazon.com/SiliconDust-HDHomeRun-Definition-Digital-HDHR3-US/dp/B004HO58SO/ref=sr_1_2?s=electronics&ie=UTF8&qid=1358376323&sr=1-2

so if you're content recording two different channels simultaneously, go with that. You may have to buy the software separately from El Gato, because I don't think El Gato sells the HD Homerun directly anymore. You can load up multiple single tuners, sometimes I have three EyeTV 500s daisychained over firewire to the same Mac, but it can be a bit of a dark art figuring out which tuners work well together. It isn't actually supported by El Gato. If I were starting over, I'd go with the dual HD Homerun.

I, too, watch the BBC iPlayer (and ITV and Channel 4) via a Mac in the living room; however, I don't know a way to "record" those streams. EyeTV won't record Safari internet streams.

Since you watch little TV, why not stay with the TiVo for OTA recording? This is my personal preference of course, but I attempted to switch to Mac-based OTA/Cable TV recording and found the human interaction differences too great to spend the time to learn. If you really want to record OTA (and/or cable and/or Netflix) you can get a used TiVo HD for $80 (I have an HD and an HDXL), or the newer Premier (retails $150). Using TiVo Transfer (from Toast) I am able transfer recordings from the TiVos to my Mac across my Airport network, and using pvTiVox I am able to transfer those shows and my ripped BD/DVD movies (as long as they're transcoded correctly) back to either TiVo.

hmmm... I do not have the problem you're having with buying a TiVo Premier. Be sure you are talking about the lowest price of the three currently available Premiers. It's the only one that has OTA capability. I cannot understand that, but cable money must be involved. TiVo website currently offers me a new Premier w/Lifetime for $399.99, or $149.99 + $12.99 monthly. That puts the equals point at 19.25 months, so the lifetime deal is pretty good, since regular cost is much more. I see it's because I qualify for a multi-service discount ( my HD is on a grandfathered $6/mo service and my HDXL is lifetime). Since you currently have a TiVo with lifetime service, I assume you should qualify for a multi-service discount also.

I'm not pressuring you. Your husband's technical expertise probably trumps my I'm-used-to-TiVo-interface preference. I just found that the issues that cropped up using the various Mac-centric video capture software and hardware were too irritating for me.

BTW: here's a $99 listing at Amazon (exclusive of service):
TiVo TCD746500 Premiere DVR - Black.