Sorry, you're going through this but it sounds like your doctor(s) are on top the situation. I was dx with TOS due to the exams done in the office, positive EMG study and positive vascular studies; too. It's rare to have a positive EMG.

Re: question regarding combining treatments.

First, I think the protocol is to try scalene blocks to see if you experience a temporary decrease in symptoms. If you do, then you'll more likely to experience relief from surgery. At least this is what I was told back when I started this journey in 2003/04. They inject some anesthetic that wears off over a few hours later. For me, the injection produced immediate relief (~10-15 minutes) and yes, the pain/symptoms gradually returned 2-3 hours later. I think it depends on the doctor as to what medication is injected so others may not have the same experience.

In your case, if you haven't seen any real difference in 6 PT visits, it might be worth trying the shots. If the scalene block works, then they may suggest a botox shot into the middle scalene. The effect of botox is supposed to last about 4 months (per my doctor). For me, it lasted almost one month which surprised my doctor and had her switching from the "conservative camp" to asking if I was considering the surgery. The complete relief from the symptoms for only a month was worth the shot of botox. Again, it supposedly shows if you're a good surgical candidate if you experience relief.

Combo of PT and shots:
For me, after the botox shot was given, I was sent back to PT as it was considered the ideal time to try to improve everything while the middle scalene was temporarily out of commission.

Three months after the botox shot, I had the surgery and haven't looked back, nor regretted my decision. I have been symptom free on that side for 6+ years now. I do have TOS on the other side due to a cervical rib and I am seeing the gradual increase in symptoms.

To make a long story short, the scalene blocks are a good diagnostic tool and should be done. You can ask them more questions about how long the effects of the shot lasts, what medications are used, etc.