If the DAC is the same, how different do CD transports sound?

I'll add a more detailed answer than I did before.  

CD transports do not do any file conversion or format changes that can color the music.  so it is all about implementation.  

The data on a CD is very dense so the mechanical components to read them have to be good.  that said, mass production has resulted in readers that can do it for $20.  So it all comes down do accuracy:  are they dropping bits and are they introducing jitter/clocking errors. 

Challenges include mechanically imperfet discs, wobble, speed control (the reader has to vary rotational velocity as the disc is read from inside to out), and laser control.

Bottom line is, a well made CD transport minimizes all of these but obviously there is less to be gained here than in , say, a DAC where there is tremendous opportunity to add color (or whatever you want to call it) to the music.  In fact, it may be impossible not to.  So focus on the DAC first.

Jerry

They should be very similar.   You've hit on a key point.  The main difference in the sound between CD players is the relatively cheap onboard DAC that each uses.  Eliminate the DAC and now you've eliminated most of the variance.

So it comes down to which CD transport drops the most bits and introduces the most jitter.   Good CD transports should do very little of either so it should be hard to tell them apart.

Jerry