I use the Aleph P through Nordost Red Dawn to Aleph 2 monos through Red Dawn. This amp system is quite fast, detailed, ULTRA-quiet, and linear. I too checked out the GFP750, and despite cousin Wes's review in S'phile, I was so put off by Adcom's poor customer service and the knowledge that Nelson simply sold them a design that I chose to buy a used P for $1800 instead of a new 750 for $1200. Nicest remote in the world, too!
The Akeph 2s pack 200w/ch into 4 ohms, so I don't experience the anemic bass some ascribe to the smaller Alephs. Far from it, as they power those incredible woofers in my Parsifal Encores to prodigious orchestral groundswells.
Alephs will also run in a dead short, and supposedly are indestructible. I would think that a used P and maybe an Aleph 5 stereo could be had for under $4k; $5-5500 with monos. I can't imagine I'll ever up(?)grade.
Some have criticised the P as being uninvolving. My experience is that it is simply extremely quiet, dynamic, and especially LINEAR. So if you need to "flavor" your system with a tubed pre, etc., then a P is not a good choice.
The P is SO revealing due to vanishing noisefloor and one-stage amplification that cable changes upstream are easily heard, as well digital artifacts that some creamier preamps can mitigate. Now that I'm running an ultraclean, resolving
front end (EC EMC-1) I no longer can fault my system for being ruthless up top. A much higher percentage of recordings sound great!
To capsulize, the Aleph combo will reveal the transducers' virtues and foibles at the ends of the chain quite clearly.
You probably love your speakers. The Alephs can do no harm there. I would then concentrate on a front end complement that is complimentary (oy!).
And then fine tune with cables. Just my experience, but it worked well.
Good Luck.