This is my opinion, I would go separate, get a good power amp, they don't change and they will not be obsoleted in 10 years. Get a preamp that have all the inputs. There are things on the preamp that can be obsolete. I know you don't care about the DAC and other digital stuffs, but chance are higher the preamp part will be obsoleted in a few years. YOu have a power amp, that's the foundation, then you build on it.
As for power amps, high rated power is NOT everything. And NO, all amps don't sound the same if they are not clipped, particular if the speaker is 4ohm and known to be hard to drive. According to Scott3886, Martin Logan ESL speakers are one of the hard to drive, I can tell you my JM LAB Spectral 913.1 is another that is very picky on amplifiers. I general speaking, I'd look for amps that have big EXTERNAL heatsink. As for brands, go listen to it. Borrow one home and listen for a day or two, they do loan out amps.
To me, it's more important for the amp to be able to drive 2ohm load than having 200W+ power. Unless you like wall shaking loud, don't need to get high power amp. There is trade off of max power and performance at low power. eg. I don't listen loud, I only use a [email protected]
amp , but is high bias class AB so in normal listening level, it's a class A amp. So louder is not better.