Importing and exporting projects between Ardour and other DAWs?

I’m looking for the best way to move projects/tracks between Ardour and recording software on other computers. (My band records mainly on my bandmate’s PC into Sonar, but I do a lot of recording at home on Ardour on my Mac that gets used on our CDs, including overdubs and main tracks. He can’t use Ardour. I can’t use Sonar and - even if I could - I prefer Ardour.)
The dream, of course, would be that there is a way to save entire projects in some ‘universal’ format, to eliminate repeated exports, imports, and the inevitable tweaks that seem to come with them. I realize this is unlikely and I’m not holding my breath.
Failing that I wonder if anyone has advice on how to transfer individual tracks most efficiently and what exporting options are best to keep the quality I get in Ardour when my tracks are added to the other software.
I’m running the latest version of Ardour on an duo core intel Mac, OS 10.4.11. He’s on an Acer running XP.
Any thoughts are appreciated.

The ‘universal format’ is Broadcast Wave’s, which Ardour handles very well. I guess there won’t be any ‘session formats’ that are transferrable.

Regarding exporting to other software, you should do as little changes to the original material as possible.
I.e. if your Ardour session is running 24bit@48kHz you shouldn’t dither and/or downsample when exporting, assuming the other program can handle the files.

Other than that, I suggest you decide on a “master” system, meaning that if the Sonar system is the master, he can give you an mp3 of his session or whatever, and the only thing you do is add the overdub tracks in whatever format he’s able to import and that imposes as little processing as possible on your side.

if your Ardour session is running 24bit

Don’t forget JACK only works with 32 bit floating point samples. You actually have to convert to 24 bit when exporting if that’s what’s required. If Sonar handles 32-bit floats, no problem, otherwise you need to convert.

peder and jrigg,
Thanks to both of you for your thoughts. Now I have a better sense of what to look for in his program to ensure better conversions. Much appreciated. Cheers.