Monoblock amplifiers vs a stereo amplifier cannot improve what is upstream.
My limited experience with using a DAC or music streamer as also a preamp is that a separate preamp seems more live than DAC/streamer only.
I run the Luxman C900u. It is placed in front of the Weiss DAC which previously was used as a DAC/preamp. The result was a far more dynamic reproduction.
Hope that contributes positively to your search.