Speakers for a Krell Vanguard

Just picked up a used Krell Vanguard to replace my 23 year old Krell KAV 300i (It’s getting old, like me, so I thought it was time for a change.) It is powering a pair of Thiel CS 2.2 speakers (also 23 years old.) I would appreciate any suggestions on speaker improvement. The room is a fairly large rectangle with little in the way to absorb sound. It houses the living room on one end (2/3) and kitchen on the other 1/3.) all of my cables are high-end. 

The new Vanguard has improved the sound of classical orchestral pieces, which were a bit muddy sounding with the 300i, and added a bit more shrillness to some of the pop and jazz pieces I play. 

For any of you out there with a Vanguard, I would appreciate any suggestions to improve the sound; either different speakers or additions to my Thiels (like a subwoofer) that you think would improve it.