Since you're not interested in infotainment or safety tech, which "luxury car" features are you seeking?
If you asked for sporty handling rather than a smooth suspension, I'd suggest the Infiniti G37. But I'm not sure it will ride smoothly enough for your taste.
The Hyundai Genesis has the look, presence, and features of a luxury car, and an excellent audio system (in those with Lexicon). The issue with a 2012-2014 Genesis is I like the 2015+ Genesis a lot better--it's a truly outstanding car. But a 2015 will probably cost about $30k at the moment (unless you find a really, really good deal on one, in which case grab it).
I don't know how reliable the Kia Cadenza has been. Probably pretty good. But it could be a very good used car for what it costs, if you can find one.
Finally, the 2014 Chrysler 300 (and related Dodge Charger) have been reliable in our survey so far. I really like how these cars ride. They're less refined than the Cadenza, much less the Genesis, but also probably cost quite a bit less.