I have a couple of these amps and am heavy into vinyl. I can tell you the phono stage,.. IF working properly... is better than any built-in stage in any current Home Theater amp. You would have to spend $100 for a pcb and parts to build a modern Hagerman Bugle phono stage kit to better it, and thats probably almost half of what you paid for the entire AU-717. I built one and wired it into the stock location. BTW, on the 717 phono board, resistors R49 - R52 can burn out. If one resistor goes, you still get sound, but distorted. If both go on the same side, you get no sound.
The one thing about vinyl.... for it to really beat CD sound, you generally need a fairly expensive phono stage and cart to get there. But when you do, it sure is sweet.
Scott T.