I've been to Jax a few times over the years. Usually as a younger person, out with family and friends for dinner. But as an adult, I came to appreciate it even more. My husband and I spent our first Valentine's Day as a married couple, there. It was somewhat crowded, but we didn't have to wait too long for great seats. The live music was a bit loud (though we were seated almost right on top of the band), but it was great. I'm not a huge fan of Jazz, but it was perfect for the romantic ambience of the evening. The dinner was delicious, the staff was very courteous, and the extras they gave out for Valentine's (I believe it was either flowers or balloons- gosh it's been ages!), were sweet.
If you want a nice sit-down restaurant, with frequent live performances, I do recommend Jax Bar and Grill!