Tube or solid state, low power or high power?
I own a few of both integrateds and monoblocks/stereo amps with preamps. It's a real toss up if there is a significant advantage at $2,000 price point if you really search for the best. $2k on the used market is where things really start to get interesting in both camps.
The primary advantage for seperates would be isolation from errant elctrical fields and dedicated power supplies for each gain stage. (though, passive preamps negate this). But, then the topic of interconnects come into the question. And that lends other headaches and costs while looking for proper "synergy" between the three components - the right preamp with the amp(s), the right IC's, etc. With integrateds, you get exactly what the manufacturer intended in one chasis - simple, no headaches.
In my system, the seperates have had the edge for performance once dialed in. My Welborne DRD 300B monoblocks amps and passive Bent transformer volume control (TVC) outperform my Audion Sterling EL34 integrated amp and Almarro A318B integrated.
But, I have also had an Audiomat Arpege Prelude integrated tube amp in house for a bit and it was glorious. Really could keep pace with just about any seperates in sheer musical enjoyment(though, it's PP and the others are SET).
Although,if you have the room - go seperates. They provide a greater platform for experimentation and upgrades.
In the solid state camp, a pair of Monarchy amps (SM-70 Pro
, SE-100 Delux
), ~$600 & ~$850 respectively, with a FT Audio LW-1 passive premplifier
perform far beyond their price point. Or, try a Placette passive preamp(~$1k). The Monarchy and either of these two pre's will be absolutely incredible in the speed, dynamics, and transparency department.
For a little more "flesh on the bones", try a nice tubed pre with the Monarchys. Something like a Blue Circle, Audio Research, BAT, etc.
I'm a tube freak, but that's whole 'nother can o' worms to get into.