Phono preamps are a little trickier, because some moving coil cartridges require particular kinds of preamps. I remember I had an Ortofon MC cart that wouldn't work with anything buy an Ortofon preamp. But in general, it isn't difficult to create a phono preamp that applies the RIAA curve and boosts to line level. Unless something is really funky, one should be as good as another. I realize audiophiles go monkey-crazy over vinyl stuff, But when you're just raising something up to line level and applying a hard wired EQ, a preamp should be transparent. The noise on the LP will dwarf any noise in the preamp. (I'm sure a vinyl nut will show up soon to loudly proclaim that only thousand dollar preamps are good enough for analogue...)
The kind of preamp where specs matter is microphone pres. When you record, you need as clean a signal as possible, because you will be pulling levels up in the mix. That low level noise makes a difference. But it isn't like that when you're just raising it a bit to a fixed line level.
My guess is that your fancy phono pre is just a little louder than the one built into the Sony. If you just raise the volume a hair, they will be the same.