8 channels ... Both types have 9.1 channels for Theater experience and are THX - EX certified. In fact they are tops in professional equipment.
Rule of thumb car audio is second rate over professional studio equipment. The only time I use fiber optics is through our backbone links. Car and Home Toslink connex are filled with judder. Professionals use hard wired connex, HDMI, Coax, Scart, or balanced analog line cables.
I just find this thread funny to hear you have spent a lot of money on equipment and tablet, and want to use toslink and above all use USB, which IMO cannot pass the bandwidth for true 7.1 sound without judder. Plus you are doing multiple downstream conversions when HDMI allows pure digital to connect, so using a MHL HDMI adapter allows untouched data to be available to your processor. I would not spend top dollar and not have HDMI digital in capabilities or attempt at limiting myself with Toslink. It is not that I am telling you your doing it wrong, as it seems that you expect the processor connection that you chose to be clean, when it is not.
http://en.wikipedia.org/wiki/TOSLINK
http://www.allaboutadapters.com/hddodtsdihdo.html
Enough said about this, you wanted to know how to connect your tablet and make the processor work. I gave all that I can to make it work for you. Its up to you to figure out how you are going to utilize it.