Mcintosh sound

If you're planning on driving your Apogees, then you'd have to choose the 6900 which has Autoformer outputs and can drive loads down to 2 ohms. You would also have to make use of the built-in MM phonostage to justify the added expense of that feature. Ditto the equalizer. Ditto the power meters.

Keep in mind that a system's sonic signature or character is 85% a result of the amp/speaker combo. The preamp's main job is to direct traffic and otherwise keep QUIET! Therefore. I suggest auditioning various amps with your Slants using your existing preamp and phono preamp for now. Then slowly upgrade those as you can.

I don't dislike (the idea of) integrated amps, but unless you're contemplating a smaller unit for the bedroom or the office, you could be investing a lot of money in a component that would limit your flexibility, forcing you to throw the baby out with the bathwater in order to make a future upgrade.
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You know I don't think the integrated is such a bad idea. The lowest prices you are likely to find are for those. In addition you won't have a problem match pre to power amps fidelity. I have contemplated the same but enDed up with a complete extravagance. I have the smallest power amp they made in the 70s called the MC2505 all of 50 wpc but it has variable gain which in practice work as attenuators i.e. with one source it's like an integrated but dual mono. The sound is I think a bit on the wieghty side almost indelicate and above all authoritative and functional. I keep the runt of the litter to power only my Klipsch Speakers a very synergistic combination indeed but I have my main systems using JM/Focals and Von Schweickerts. So it is a luxury.
The little amp feels like and behaves like an amp twice it's strength and yes it has bass but not the Krell iron fisted bass just no doubt if you have a big woofer these amps welcome them not shirk them.
I echo getting the autoformers for panel speakers not sure if it has the transparency you want with an anti meltdown circuitry. Never tested anything other than cones and domes. still this pugnascious amp succumbed to the previous owners playing too hard and took out some strength on one side somehow a very unusual situation for an amp that exudes an unbreakable air.

Warm, lush, enjoyable, bloomy, not neutral.