Since the tempest has two sets of outputs the way that I did it is like this:
Go to radio shack and pick up an RCA A/B switch.
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=15-1952You'll also need an extra pair of interconnects.
Run HT outputs to one side and audio to the other, then the sub cable to the sub amp - a single cable is fine from the Denon to the switch, just make sure that you put the cable to the sub on the same L or R as the input from the Denon. The only issue with this is you won't get the bass management of the Denon in 2 channel - the full range signal will be going to your sub, however, if it has crossover adjustment on the sub amp you're all set!
The hardest thing after this is remembering if you've switched it to the right thing! I remember mine by putting HT on the "B" side - as in "B movies".
Is it recommended that I even use the sub with full range speakers?
It is if you like the sound better!