I don't know, I find the TP to be very satisfying on digital out.
Have compared it to several decent CD/SACD players and like it better by a decent amount. Granted, not to super high end CD players. And also to a non-modded Touch - no comparison imo. Granted, I use a decent power cable, and decent digital cable from TP to DAC and I'm careful to tune the Squeezecenter configs.
If the Transporter is only serving as a bridge to a USB input on a good DAC, and not part of a whole home music distribution system, and your DAC has a reputable USB input, I'd say going straight from computer to DAC on USB is a good option also.
