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

The DAC will make the most difference. In my experience.
With a caveat…you must use a decent CDT…something like the units I mentioned above. Don’t waste money on a good dac if you plan to drive it with a $99 universal player from early 2000s. Just like anything else in this hobby, you can get by but to realize a full potential of any given component the rest of your system must be on the level. 
 

I posted this on another thread :

Transports are not all the same SQ wise and will either hold back or release the potential of the DAC. Benjamin Zwickel, Mojo Audio DACs, clued me into this when I was purchasing one of his ,and he was correct. I went from Cambridge CXC to Simaudio DT 260 and the SQ materially improved. Check out the threads on the top Project transport or the Jay’s transports and you will find similar experiences. Also, when you go beyond the likes of the Cambridge or Audio Lab transports one of the digital output connections might be optimized for SQ so you may want to have a DAC that accepts that connection. I initially used the SPDIF on the Simaudio and it sounded very good. However, out of curiosity I asked Simaudio if one of the connections was optimized for SQ and was told the AES/EBU was. The result was a further uptick in SQ. I believe the top of the line Project is optimized likewise, though folks using the SPDIF connection appear to be very pleased with its SQ. I don’t know if either of the Jay’s transports have an optimized output.

I'll further add, it's not about bling , expectation bias, status ranking, and the rest of the  commentary.  It's about the resulting SQ. Try them firsthand and decide for yourself .

When I compared my Sony HAP-Z1ES streamer to my MBL 1621A transport, I could not distinguish a difference when they were running through the same DAC, an MBL 1611F. The rest of the chain was an MBL 6010D pre-amp, MBL 9007 monoblock amps, and MBL 111E speakers. I played the same song through both simultaneously and switched back and forth between them. They sounded identical to me. 

I sent the output to my headphone amp as well and kept playing music and switching between sources on the fly. Again, I wasn't able to detect a difference.

This was my experience: others may have different experiences. But in my system, my $2,000 streamer equaled my $20,000 transport.

I liked this video and the comparison. The players were level matched using a voltmeter and the listening panel seemed to be skilled. These and other details show that there was some thought and care that went into this experiment.

The conclusion drawn about all the transports playing through the same DAC isn’t surprising, just common sense.

@zlone

Is a transport + DAC equivalent to streaming? Pretty much. Either way, the digital data is being transmitted from point A to point B in a real-time fashion.

@yage Thanks for watching and commenting thoughtfully. I am curious whether Mr. Lovegrove feels satisfied that a sufficiently high quality of transport (or player used as a transport) was represented in this listening trial. He went to a lot of trouble to do this experiment -- did he miss a chance to use the kinds of units people here are convinced make a difference? (In fairness, I am not sure if any here have done the kind of controlled listening test that Lovegrove did.)