Passive Preamp works with Dynavector p75?

It worked with my Passion Ultimate passive but my Meridian 605s only need .5 volt for full output.

I just noticed that your McIntosh MC 122 has level controls in the rear that can be set at .8v sensitivity. You could try that and see if it's enough gain for the passive preamp.

Try running the P75 directly into the mc122 with no preamp at all. This will tell you what the highest volume level that you will get with a passive pre wide open will be. Adequate volume is only one of the considerations when going the passive pre route, but this would be a good start. Be careful that you don't overload the speakers, but with the Maggies' lowish sensitivity, I doubt you would have any problems. You will probably be surprised by the increase in clarity and refinement, but very possibly also disappointed with the lean and undynamic sound. Worth the experiment.

What is going to be important here is the input sensitivity and voltage gain of the MAC. My friend has the P75 going into a Sowter based TVC into a CJ MV60 SE. He is using a Dynavector cart, the 17D2 I think. This works great. However his speakers are GMA Europas which are more efficient than your MMGs too. I still say my first sentence in this post is going to be key for your success.

Shakey

It will probably work, but how well is the question. Input sensitivity of .8V is a good start, but the gain level has to be taken into consideration too. Also, input impedance on the amp is 10k ohms, not usually ideal for a passive preamp regardless of the source IMO (unless it is a buffered passive like the Pass B1).