Hello! I started to post this asking for help, then resolved it myself. Hurray for me!
Most people may already know this, but with my Windows 7 system I have to plug the headphones before
opening the launcher in order for my Logitech G330 USB headphones to be shown in the Preferred Playback devices shown under the "Audio/Joystick" tab in my 5.5g launcher. When I opened the launcher first, I could not get any Freespace game sounds through my headphones. I could hear other sounds, such as Spotify, through them even as FSO continued to pump out sound thru the speakers.
Just thought I would post in case anyone else runs into this issue.