Does the Transport make a significant difference

The Transport and specifically the jitter in the digital signal is actually more important than the DAC.

What you have is a major mismatch in performance. You have two options:

1) buy a really expensive transport, say $3K+

2)add a Synchro-Mesh reclocker to your transport $600 plus power supply

The reclocker is not a Band-Aid and will make your transport totally important. The cable from transport to the reclocker is also unimportant. You can use the cheapest plastic toslink does not matter. 30-day money-back guarantee, less shipping.

The biggest advantage of the reclocker is that it isolates the clocking from the DAC and transport noise. It is powered from its own isolated power supply. IT is designed specifically to isolate both inputs and outputs and provide signals with minimum jitter. You can use a really good low-noise, fast-reacting DC supply like the Dynamo to power the reclocker and you will get world-class results. Reviews and customer feedback:
http://www.empiricalaudio.com/news-and-reviews/synchro-mesh

Also I recommend to replace your coax cable to the DAC with one that is unbeaten in the market place, my BNC-BNC with AC adapters. I make very little money on this cable. I created it so that I could provide my customers with a reasonably priced solution.

Steve N.
Empirical Audio

"I'm assuming changing preamps will take me to yet another level"

It certainly can, but probably not for $2-3K. Good preamps start at ~$10K unfortunately. You might consider a passive transformer linestage. The Music First is very good at around $4.5K.

The fact that driving your DAC direct to amps does not sound better is probably due to either:

1) the DAC does not have low enough output impedance to drive amps
2) the preamp provides a level of isolation between the DAC and amps
3) the volume control technology in the DAC is inferior to the preamp

The likelihood is that the problem is #3.

The best possible of all worlds is to eliminate the preamp without using software volume control. Instead, use a volume technology in the DAC that does not add distortion or noise, such as this:
http://www.empiricalaudio.com/products/overdrive-dac

This volume technology is like no other DAC. There are actually no parts added for the volume and no analog circuits being adjusted. No bit decimation either.

The DAC is expensive, but replaces preamp, computer interface and DAC. All you need is a computer, amps and speakers. It recently won a multi-DAC shootout on Audiogon, beating out PWD, Directstream, Mietner MA, Lampizator, APL and others:
http://forum.audiogon.com/cgi-bin/fr.pl?ddgtl&1398132150&&&/Absolute-top-tier-DAC-for-standard-res-R

There may be a demo unit for sale soon BTW, at a discount.

Steve N.
Empirical Audio

Ray - he is probably just removing veils, jitter and distortion. When you do this, the imaging becomes less diffuse and things seem to "snap" into focus, appearing to relocate. They have not really moved, just focused.

Steve N.
Empirical Audio