iTunes 6 + Photoshop = The solution to this problem. Wanting Max to have a "1 Window" interface doesn't mean one window for everything, it means one window per.... function. In other words, one window for cd ripping/encoding, and one window for file converting. Here is my mock up. Its not a .nib, its all photoshop.
See each CD you insert shows up in a similar way as it does in iTunes. Only as the songs get ripped, they move over to the encoder on the right. Unlike the current Max setup that keeps a million CD windows open at a time, the left CD column of my UI only shows actual physical CDs in your computer. When they are done being ripped, and all the songs are added to the encoder, the CD ejects and disappears off the on screen list (possibly with a neat apple like ripple effect

).
I figure that based on the MB in the encoder queue, you should be able to get a fairly accurate ETA for processing the whole queue. It should be going backwards as you added more and more CDs but once the ripping of CDs stopped, the encoder could count down nicely.
Another thing I thought of that isn't directly related just to my UI mockup, is that when there is a choice of tag info from the tag database, theres no reason why you can't start ripping anyway, since all the AIFFs are stored with coded names anyway, the tag data could just be applied once the encoding started.
The converter really only needs a one column windows. A list that you can drag files directly too. Then that list IS the encoder window, that Max goes through and encodes, and takes files out of the list once they are done encoding.
And what would also be great to integrate is the crash recovery techniques I put in a thread earlier today.
Also I started to get tired of photoshoping and I left out the indicator(s) of hard drive space in the Max window, that is a MUST. And I just put two buttons at the top but of course as many as you have just go across the top there. Both the ripper and the encoder would need to be able to scroll. I forgot to add teh scroll bar to the ripper column and didn't feel like adding it when i noticed. Also the ETA times are all screwy, again I just didn't feel like trying to come up with real looking data.