I recently took delivery of a T4 (UK spec), and this has an auxilliary input in the centre arm rest locker. This works well for my iPod and I can't see why it wouldn't similarly work for your cassette player. I don't think I ever put a cassette into my last car and I won't be missing the lack of it here.
The one thing I am finding the lack of is 12V outlets! Just the one in the aforementioned locker is wholly insufficient, not to mention in the wring place. I need one on the dash, preferably up on the top of it, to power the Tom Tom Sat Nav and the Bluetooth mobile phone hand-free while the locker one does the iPod! Has anyone tried fitting one?