Just got an HTP 201 Invertig

Well, you certainly will not be able to weld Aluminum with DC. You need AC, at the least, or square wave AC to TIG aluminum. The reverse polarity uses Argon ions to bombard and clean the aluminum surface.
Tig IS hard after all. Tig welded 3/16" rusty steel rod to I'm in the same boat. I have a Lincoln square wave 300. I have made actual Tee welds in aluminum sheet, but there were only a few good sections, and lots of holes and weak welds. Practice, practice.
I made the mistake of getting pure Tungsten electrodes at first. After having lots of trouble, and being guided by the experts that pure Tungsten was pure trouble, I dug out some thoriated electrodes I found years ago, and the difference was amazing! I didn't get blobs all over the electrode, for one thing.
Jon

Absolutely. AC is a requirement for successful AL welds.
I think it is easier with filler rod. Then it becomes more gas welding where you can sort of push the puddle around.

There's a lot of info on sci.engr.joining.welding that you may find helpful. As 316 SS is mostly steel, your new alloy isn't quite there yet. If you manage to weld Ally to SS, now that would be a neat trick.
John