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

It will be affected by how clean the digital signal is from the transport to the dac.

Most deniers are oblivious to the fact that the “digital signal” going over a wire from transport to dac is an analog signal representing the digital data. Noise on this analog signal caused by a poor transport or bad cable will infiltrate the dac. better dacs can filter some of the noise but filtering is not perfect because electrically everything inside the transport and dac are connected. Nothing is perfect but some equipment and cables are better than others. 

Wanted also to add this factor for transport differences…

the optical laser detector inside the transport is an analogue electronics device which is changing its output continuously as the laser light dims and brightens. 
 

Electronics on the pc board later determines if it a 1 or a 0 based on the analog electrical signal from the laser optical reader and sets 1 or 0 based on a threshold. 

Where I am going with this is that another source of electrical noise in the transport is noise that the optical laser detectors is picking up between the high and low points reflections of the CD aluminum pits. This is “light noise” between the high and low reflection signal and is the scattered laser light inside the transport enclosure. 

Everything is connected electrically and better transports will filter this noise from from the optical sensor from getting into the signal path. No filter is perfect but they can reduce noise.

this is why darkening the edge of a CD with a marker pen can improve sound reproduction by reducing the scattered light inside the transport which reduces the “light noise”.

if you followed this and have a resolving audio system would like to hear back if you can try use a dark marker on a cd edge and listen for differences.

I can on my mid level high end system though I mostly stream now.