"If the DEUS has four frequencies that are used one at a time then what makes for the detector locating deep coins such as the multi frequency detectors."
As far as I'm aware, it depends on the machine and the soil it's being used in. Multi frequency isn't a guarantee of more depth over a single frequency machine, even in bad soil. In my middle-of-the-road Northern Ohio ground, the Deus with stock 9" DD coil goes about as deep as my dual frequency CZ with 8" concentric; and that's a pretty deep machine.
"Also the lightweight headphones or the heavier padded ones."
I love the backphones; very light and comfortable, and they allow me to hear everything that is going on around me. They are not as rugged as the WS5s, however, and those with larger heads may find that they don't fit as well. A lot of people prefer the heavier headphones for a good fit and also to block out background noise.
"Also the coil sizes -which are best for general coinshooting."
Some prefer the 13" coil for better ground coverage and a little bit more depth. Others prefer the 9" for better target separation in trashy areas. The upcoming 11" coil may turn out to be the best combination of both.