Is this a new issue, or is it only happening with v1.7.0.6?
After changing the default audio device, was VoiceAttack restarted before playing sounds?
I don't have this issue on my machine(Windows 10, Integrated Components, VoiceAttack v1.7.0.6/v.1.7.0.7); Playing back through multiple devices, even simultaneously, seems to work fine.