Heated steering wheels have only become somewhat common in recent years, so you might not be able to find a larger European car with on in your price range.
If the A6 back seat is too small, it sounds like it's time to look at the A8, 7-Series, and S-Class.
Scratch that, just had a thought out of left field: BMW 5-Series GT. They've been a sales flop, but more-or-less combine the handling of a 5-Series with the rear seat room of a 7-Series and the practicality of an SUV. The first model year with the six-cylinder, 2011, is within your price range.
Returning to sedans, you might want to at least test drive an Infiniti M. They have tighter steering and handling than most Japanese cars, plus a roomier back seat than the midsize Germans. The 2006-2010 feels roomier up front than the current generation.