Well I'm pretty sure you can put the 205/55R16's on your stock XRS rims. There's a guy at work who told me that you can go +/- 10mm either way (JL you know who you are.

) He had a set of Celica GTS rims (which usually have 205/55R16 tires) but with the stock XRS Michelin summer tires (195/55R16).
I'm not sure about putting aspect 50 tires. I presume so since that just means you have a smaller sidewall.
Whoever is mounting your tires should have a good idea on whether you're still in spec or risking a problem with rubbing.
GL