Does anyone have advice for using an external sound card?

It looka like this one is the latest in the Win 7 64 bit (and 32 bit) listing.

Model Content Page

The 8.54.... version is listed for Win 8.

I still recommend installing the latest version on the Toshiba download page for Win 7.

The latest version for Win 7. 8.51.2.51

Model Content Page

I'm out of suggestions. However, I still think its a problem in the PC and not the sound chip but something else causing it. You can try a USB connected external sound "card" as you originally considered but no guarantees that it will fix the problem.

I'm in Florida, not Nashville. I was there in the early 70's and had a day job as the Amplifier tech at a lower Broadway music store (across the street from Tootsie's that is no longer there). I was learning the pedal steel guitar back then but did play some jobs around Nashville including some of the lower Broadway clubs. The "R.O.P.E" is a fraternal organization of entertainers including singers, musicians and other industry personnel. I have a home recording studio here in Florida and have also worked Florida tours with some of the Nashville singers. I did 7 winter tours with Tommy Cash and two with George Hamilton IV, plus single shows with others including David Frizzell, Jack Greene, Bobby Bare, Ray Pillow and others. Tommy Cash was my sponsor to get into the R.O.P.E. organization.