hmm, if it is TOS or something like it...
the bands & weights and such (active on your part) type exercises should wait until all, or at least most, of the symptoms /pain/tingling are resolved by passive means first.

What kind of muscle stim? do they use IF stim (interferential (sp) ? or another type? IF stim is nice as it can be set higher without the tingle /zapping of other stims - and if it has the right options/settings it does feel like someone is massaging all over your back - if it used on the back anyway.

Any massage?
manual trigger point work? *If TrPs are present they have to be released before any stretches or strengthening will help*
posture evaluation?
forward head/shoulders?
passive stretches to open the chest/drop shoulders?
my profile has pics of 2 styles of those in my album - they are up in the useful sticky thread also.

I'm not sure if there is any time line for scar tissue issues.
I think some tend to have it and some don't have problems from it.

Sharon Butler's gentle stretches were a real help to me - plus she has really good info about fascia &how it gets damaged and how to repair it.
she has a book (in libraries) & a website.