It can be "notchy" shifting from 1st. and 2nd. sometimes, and that mostly happens in the 2004 models. It's no big deal, and usually gets better as the tranny fluid warms up.
As for changing an auto into a manual, like TVT said, it would probably take a new computer, and a re-wire.
If you could find a wrecked Crossfire in a salvage yard with a 6 spd, you could probably get everything you need to do the swap from a donor car. It would take allot of work, but could be done.
There have been several owners from "down under" here on the forum over the years, but I can't remember if any of them had 6 speeds, or automatics. Does anybody know if any manual shift cars were sent to Australia?
Start checking the salvage yards, and see if anybody has a "donor" car first. Keep looking for the real thing as well.
I have an 04, 6 spd. and completely love it. But if the ONLY way I could have a 6 spd. was to build it myself, I'd probably take the easy way out and go auto. But that's just me. Good Luck.