I use the MC-402 with the 3.6's and get superb sound. I have heard the 501's as well in a direct comparison with the 402. At regular listening levels I could not hear any difference. If you are buying "New" from a dealer my guess is the most influence will lean towards the 501's for the bigger & better sale.
If you want to spend 501 type money give a listen to the MC-2301's mono tube amps as well. See if they do the trick for your maggies.
If you want to spend 501 type money give a listen to the MC-2301's mono tube amps as well. See if they do the trick for your maggies.