Welcome to the forums.
I'd skip the passive bi-amping of the speakers, that's mostly marketing nonsense IMO. Read this
http://www.audioholics.com/frequent-questions/the-difference-between-biamping-vs-biwiring
The Onkyo 706 has a built-in phono stage, so just connect the tt to the phono inputs (assuming you have an MM cartridge and standard rca connection....but what tt and what cartridge is it?).
That dac seems to be primarily for a usb output from a computer, and has headphone amp output from a brief look. You may be able to use it well enough as an interface to your receiver as well via usb/optical/coax digital output from your computer to the dac and analog output from dac to the receiver.
If your mac has digital optical or coax outputs I'd just connect those to the appropriate inputs on the receiver and use the receiver's dac and eliminate the external dac.
ps That receiver may not suffice amp-wise at very loud levels; if the avr goes into shut-down you'll know
