I think you are misunderstanding. It doesn't matter how you are paid, the problem is that now you are in the US, when before you were not,
As such, you are now performing work for a US company on US soil, thus you need work authorization.
That will require either TWO TNs, or TWO H1-Bs. As Jo pointed out, your 2 H1-bs would have to be as an employee. Your 2 TNs could be either.
So, if you get an H1 for firm A, then you work firm B only as an H1 employee . If you remain a TN, you can become either a contractor or an employer, but will need the second TN.
The manner in which you are paid as a contractor has no bearing on TN, but it is completel forbidden on h1.
Languishing in Lincoln -No More!!