Welcome! Have dedicated summer and winter tires, no chains necessary unless you are planning on plowing Loveland and Bethoud passes for CDOT. Search this Rockies/Midwest forum for tires and driving routes.
Also (closer to Denver), if you can get a way from traffic, I also like Deckers Rd near Pine (https://maps.google.com/maps?q=Pine,...orado&t=m&z=11
) and Rampart Range Road https://maps.google.com/maps?q=Pine,...orado&t=m&z=11
My personal tire favs:
IMO Blizzaks are overkill in Colorado (especially for xi) because it is dry here, even in winter. These PA3s handle better than any A/S tire I have ever had, but are much better in snow. These are perfect for your XI.
As for the Lexus, get dedicated winters again. Blizzaks for extra safey, or the PA3s again.