The Best Preamp is no Preamp?

I'm using just the amp and a dac and I think it sounds great. For others maybe not but I'm happy with it. 

Like everything - depends on the preamp.

A quality active preamplifier is much better then a passive dac to amplifier ,

especially if you have a Quality vaccum tube preamp the signal is amplified and transformer ,choke gain stage when under load is bigger soundstage ,deeper and better imaging ,adding the vacuum tubes adds an added dimension ,having owned a Audio store ,as well as Audiophile for over 40 years I have had every combination 

and their is plenty of ample proof putting a Quality preamplifier at least a  $5 k lie stage preamplifier is far better then use dac to amplifier you need to spend money 

to get mid Audiophile quality .

Then the answer is, what ever works for you. No final concreate answer, many variables that will determine many diffrent ways.

As to me, Pre-amp is very very important, but of course you need a very good pre-amp otherwise possible answer would be to avoid it and go direct to DAC.

I had my Benchmark LA4 out of commission for a couple of weeks and was using a Denon receiver to fill the gap.  Even in pure direct mode the sound quality was significantly worse.  As per an earlier poster, I’m not surprised you found an improvement removing the Marantz from the chain.