The [Enterprise-A] comment is not correct. The dinner was not hosted in the Officer's Lounge.
The script for Star Trek VI: The Undiscovered Country, says that Kirk and his crew hosted their Klingon guests in the "Officer's Mess". The same room is destroyed by a torpedo hit on the Enterprise later in the movie.
Exerpts from the script:
43 Int. officers mess, Enterprise A window irises open reveling the stars gliding by. A hand pours deep blue Romulan ale into Gorkon's crystal goblet. Dinner well underway. Principals from both parties are at the table. Stewards keep food and drink in motion.
182 Ext. Space VFX Enterprise takes another hit.....
183 Int. Enterprise officers mess No shields this time! Explodes! WOW! Autotight bulkhead doors close, protecting the vessel from space exposure. Smoke, liquids squirting everywhere... Things tumbling off shelves, out of overheads...Doors whooshing closed!