I also transfer edited styles from PC to my Yamaha Tyros 5 by copying them to and from USB. If there's another way, I would like to know too!

I never seriously researched the DGX-670. The Tyros 5 was the first Tyros that didn't have Yamaha's "Internet Direct Connection." Additional songs, styles, and expansion packs purchased from Yamaha have to be added to expansion RAM using Yamaha's clunky "Expansion Manager" software. I guess it's an anti-piracy thing (which I understand.) But I liked the Tyros 4 better, with its Internet Direct Connection. Following this thread!

One more thought... I'm not sure whether you have tried some of the Yamaha iOS apps like Chord Tracker. I messed around with them and was very impressed. So much so that I decided not to sell my T5. FWIW.