Avery,
I do not own a QY70 but I have a PSR730, which also has a MIDI in, MIDI out and a TO HOST port. I would like to ask you a simple question: Did you use the TO HOST port with a mini-DIN8 to serial DB9 cable from Yamaha to connect your QY70 to your computer? And if so, did you make sure that you put the small switch by the side of the MIDI/TO HOST port to the TO HOST position? If you are using MIDI out, please also make sure that the small switch points to MIDI. These connections are either or, but not both. If you did the connection right, then check another cable to see if the first one malfunctions. If the seond cable solves your problem, then you have either a faulty Yamaha cable or a cable not wired to Yamaha's specs. If the second cable still fails, check to see if your computer serial/MIDI port functions normally. If all the hardware works fine separately but you still cannot make QY70 and your PC talk then you probably need to talk to Yamaha technical support people to see if they can help you.
Paul Ip