Are you saying you are looking to purchase 2 differnet Slingboxes?  I think that might be more hassle than it's worth.  You are talking about setting up 2 Sling's on the same network, it's doable but I am not sure it's worth the effort honestly.  I'd go for the Pro I think it'd make you happier.  Are you looking to Sling your HD content?  If that's not your #1 concernt just use a s-video cable to your cablebox and you will still get all your channels including HD channels just not at the best quality.  just my 2 cents....

Slingbox Pro Slinging Comcast cable and HD via Comcast HSI using AirLink Powerline adapters; Slingbox Classic Slinging Sunddenlink Analog Cable and D* HR21 via Sunddenlink HSI, using Linksys Gaming adapter.

If the Solo is HD. Then two boxes is the way to go to get two people on at the same time. But, remember, you'll be sharing the upload bandwitdth between the two boxes. So, unless you have massive bandwidth, the quality will suffer.

If you're using the coax input there should be very little difference in quality. Especially if you're viewing it remotely. Unless you can get more than 3-5mb/s in upload speed you'll never get the same quality you would get as if watching from a LAN connection. And that's just from one box. If you have two, double that bandwidth.

Seriously.. I'm waiting for an iPhone client myself. I'll take any kind of quality at this point.