I had similar issues with my SHB9000 and windows 7 x64 and though they seem resolved now that I installed the latest ASUS Bluetooth drivers, I did notice some interesting things;
1) The ACER bluetooth drivers did install, but messed up everything. All the devices exposed by the headset were there all the time, even when the headset was off, and the sound defaulted to it all the time even if it was nowhere near the laptop. The drivers installed fine though, no conflicts.
2) The ASUS drivers, specific for the BT-253 chipset, worked fine, even though the ACER ones claimed to be a newer version (I had to manually uninstall both the software and all drivers).
3) Most importantly, while experimenting, I noticed that the headphones switch from the proper stereo protocol (A2DP) to the crappy wireless headset one (the mono sound, whatever the name is) whenever I activated the microphone in some way or another. Currently, the headset is present as both a playback and recording device in the audio settings, whenever it is turned on. The recording device is the default recording device when the headset is turned on. As soon as I turn on ANYTHING that captures microphone input (even the "Recording" tab in the "Sound" settings), it switches to mono sound in order to enable microphone input. If I DISABLE the wireless microphone, or switch the default to the built-in microphone, it goes back to proper stereo sound.
In short; if you're experiencing this, try disabling the wireless microphone in the sound settings, or set the default one to another microphone. As long as the microphone on the headset is not in use, it will use A2DP and the sound quality is fine.