Hey there!! Sorry to ping a very old post, but I have no idea how steam vr works.
I have all of the files downloaded and I followed your post, the target and start field working with quotation marks and all. I feel as if I've missed something- but when I launch it from steam, it still just launches on my pc.
When I run steamvr, it does say "please plug in your headset" despite it being plugged in.. that might be a problem? I'm on a quest 3 which was OP's system and he said it worked fine. Any help would be much appreciated!!