BINGO. You nailed it. You need another Sat box to pull it off.
The Pro HD has three independent, viewer-selectable inputs:
- Tuner (NTSC, ATSC, QAM)
- Component (for HD)
- Composite (S-Video or "Yellow" RCA + audio over traditional A/V cables)
You can have different sources connected to each input at the same time. In the SlingPlayer app, you choose which one you want to watch. Since the inputs are independent, it doesn't matter what the other two sources are up to while you're watching. It does matter if the home user is watching the same source as you are.
Like your TiVO, you can hook coax CATV up to the tuner, but not satellite- that needs to be handled by one of the other input types so you can use the IR Blaster. This is because Satellite only outputs one channel at a time. There's nothing to tune. Same thing goes for CATV set top boxes.
Unlike some TiVOs, you can't use a CableCard- the only thing the tuner is going to grab off CATV is traditional analog basic channels (NTSC) and unencrypted digital channels (clear QAM). You could also hook an antenna up to the tuner and grab whatever broadcast TV is floating through the air (ATSC). Regardless of what you connect to the tuner, it will not affect the home viewer at all.
The other two input types have IR control support and will cooperate with Satellite, CATV boxes, DVD Players, VCRs, Apple's Front Row app on Macs, a whole bunch of stuff. These inputs can't "tune" anything and rely on the source to handle that. They simply accept and process whatever signal is being fed to them. As such, you'll see what the home user is seeing... and you both have remote controls ! Remote battles are only amusing the first time, and then only for a short while.
Back to your question...
Think of it this way: Slingbox is a television. Don't look at it as any sort of flexible, complex media device. It's a TV that happens to use your computer as it's screen. When hooking it up, you have the same options and limitations as a regular television.
If you look at it that way, what you're trying to do is hook two TVs up to one Sat box at the same time and watch different channels. That's obviously not going to work, each TV would need its own Sat box to make that happen.
Hope this helps,