streaming an entire transponder isnt cpu intensive, transcoding can be, but just leaving it in its original codec means almost no processing. Its impossible to say what transponders your looking at, so how many channels is upto you. But its a quad tuner, so 4 transponders x how many channels are on ...
I use a USB 3.0 hub on a USB 3.0 port on my computer to run 4 DVB adapters off one port, works fine. Now the Matrix is USB 2.0 but still should have enough bandwidth to run 4, I just never tried it. Give it a go and report back.
The card passes the video data raw the codecs decode it, so if the colors are wrong or the video is blurry it's not the card that's at fault it's either a poor video feed from the satellite or something on your end, codecs etc.