I believe the volume problem that you suspect might be more related to your pocket pc than iGuidance.
Neither of my vehicles have "stock" exhaust.
i.e. you do not want to ride with me if you have a headache. I can hear the voice just fine. I have my pocket pc at one notch over half volume and iGuidance at 1 or 2 notches over half. the volume is plenty loud on my 8125. It is infact ear pearcing with iGuidance at full volume and the pocket pc still at half.
I've used iGuidance for years and believe it is the best navigation software for your money that you can get for north america. Version 3.0 added a lot of nice new features. I was very pleased with the upgrade.