Is no preamp really better that a good preamp?

Having enough gain in a source component is not all that is necessary to get the best sound out of that component. The output stage of a good pre-amp is engineered to drive the input stage of a power amp, while any given DAC or phono stage may or may not be.

In a related topic, it is for the same reason that many listeners (no pun intended---see below ;-) find the sound of a passive pre-"amp" to lack something (see Art Dudley's column in the current Stereophile).

All true Phusis, but the OP was asking specifically about adding a separate (perhaps tube) pre-amp between both his DAC & phono stage and his power amp.

I wish it were George. The interaction will be with only an un-buffered passive pre's volume control, then. Does that include those with optical attenuators (Lightspeed)?

Yes! Well, it took a design expert, but finally a great answer. Driving the inter-connect cable---what a concept! Maybe another reason why the sound of any given cable is so system-dependent---it's interacting with the volume control in the pre-amp of every system it's put in.