The most direct connection from source to sound will give you the least distortion. Every time that I have simplified the signal path in my system, the sound has improved.Getting rid of an equalizer, simpler preamp, etc.
If an integrated amp has the same circuitry as its separates, I can't see how it wouldn't sound better than separates of the same model level. You eliminate the interconnects.
If you're talking about a vinyl only system, the phono stage is more important than the preamp, which should be essentially a switching and volume box. I have heard of a phono stage that can be directly plugged into an amp with no other input options, It has a volume control on it with no remote. Simplicity and direct connection. I didn't want to spend that kind of investment (I think it's around $16K from Sutherland- which is what he uses), but that sounds like Utopia for a vinyl only guy like me.
Is anyone aware of these types of components, and have you heard them, and are any available at a more reasonable price level?