After testing the stock rom and an upgraded radio, the sound quality remained poor.
I called Plantronics and was told that poor sound to non-A2DP headsets is characteristic of the Titan and similar recent A2DP models, but not the 6700. Apparently good sound quality is reserved for A2DP bluetooth connections on the Titan. I did quite a bit of searching without finding another solution, though I found that the problem has been reported elsewhere such as
http://forum.ppcgeeks.com/showthread...ighlight=tinny.
Suggestions included using the equalizer and DSP features of Pocket Player ($), or SRS WOW HD (free) which improved sound for some users,. I also tried changing the registry setting HKLM\\SOFTWARE\Microsoft\Bluetooth\A2DP\Settings\U seJointStereo without effect.
Some comments said that podcasts were listenable with equalization, but I found that I could only tolerate a few minutes on the 510. I think the quality varies among headset models. For example, flyers2114 reported good sound from a Jawbone 2 (
http://forum.ppcgeeks.com/showpost.p...0&postcount=32).
I'll try a Plantronics 855 A2DP headset though I hate to give up the 510 because the ability for callers to hear me clearly is most important for me and reportedly the 855 doesn't match the 510 here (
http://forum.ppcgeeks.com/showpost.p...8&postcount=28). I also don't like gel ear tips and prefer the behind the ear headset style.