https://www.flyertalk.com/forum/unit...-flyer-26.html will give you all the details - it's written from the perspective of the reverse, but the trip is the same.

I second what the others above have said - check your bags at TBIT, then walk landside to either T6 or T7, enter security there, and then walk to the Polaris lounge.

On the return it's probably quicker to stay airside, but only because it'll avoid you having to re-clear security. If you do decide to go landside, depending on the time of day it may be quicker to re-enter via T4, which is then as easy airside walk to TBIT.

And don't forget you also have the Star Alliance lounge in TBIT (as is the subject of the above post). Whilst not quite as good as Polaris, it's still an excellent lounge (at least by US standards).