I suspect that a significant contributor to the problem is the impedance match between your preamp and amp. The Primare a30 amplifiers have an input impedance of only 10K. The output impedance of the Art Audio preamp doesn't appear to be officially specified, but I found a thread in which someone indicated that it is 2K, which is too high to be ideal with a 10K load. And assuming that the design uses an output coupling capacitor, the output impedance probably rises to values that are significantly higher than 2K at deep bass frequencies, which would result in rolloff of the deep bass with a 10K load.
If your PS Audio DAC is the Perfect Wave, which has a built-in volume control function, try connecting it directly to the power amp, and see if you get better bass. If you do, and if you still want to use the preamp, you could insert an external buffer stage, having high input impedance and low output impedance, between the preamp and amp. Other A'gon members have highly recommended Tom Tutay of Transition Audio Design in Florida as a supplier of reasonably priced custom-made buffer stages.
Regards,
-- Al