Glad you found a solution,and such an affordable one at that. The headphone jack was the next thing I was thinking so I'm glad someone else brought that up. I recently went thru a similar exercise with my MIL and her TV because her mate needed headphones to hear but there are also othes in the room with unimpaired hearing.
Your solution to the USB issue is so typical of the kinds of rabbits we have to pull out of our hats these days. Never know when you'll need to some up with some little gizmo that fits the bill perfectly.
It does seem that flat panel speakers are getting worse, and also the larger sets tend to be the worst. The little 26" in our bedroom has plenty of audio headroom, but the big screen in our livingroom was so hard to hear, I hooked up a small receiver with some bookshelf speakers just so we can hear over the background din without firing up the HT gear.
Polk RtiA9's, Denon 3312ci & Emo XPA-5 amp, CsiA6, RtiA7 surrounds, FxiA6 rears, twin Klipsch Synergy Sub-12's, DSW660 & Lsi9's upstairs