Phomchick, you are under a couple of false assumptions.
Not false, you just don’t agree with them...
1: A straight line [wire] with gain is desirable
Of course it is. If all of our electronics behaved like straight wires with gain, it wouldn’t make any difference what components you selected. Of course, this wouldn’t be the best thing for the high end audio industry. As to your suggestion that a "sterile" component can be warmed up by routing it through a warm sounding tube preamp, that is fixing one kind of distortion by adding another type. If that is your thing, okay, I can go along. But the OP asked "Is there any Streamer/DAC/Preamp good enough to replace a dedicated standalone preamp?" To which the correct answer is almost any DAC will do, as the "extra" preamp is adding one (or more) of three things: noise, distortion, and frequency response / tonality anomalies. Remove the preamp and you remove those distortions.
So unless the "volume" control is really good that dac/preamp may actually alter the sound going through it via the volume control.
This is just FUD. Which DACs exhibit these kinds of volume control problems? Do the OP’s suggested DACs, the Mytec Brooklyn Bridge or Teac NT-505 have these problems? And these arguments could apply just as well to the preamp. And if the DAC didn’t even have a volume cointrol, that would be really bad, wouldn’t it? :-)
3: Many dac/preamp aren’t real preamplifiers but are just the output stage of the dac with a volume control and therefore may have difficulties driving an amplfier or longer cable runs optimally.
More FUD. Please suggest a modern audiophile DAC that cannot adequately drive a high impedance amplifier input.