The Marcus is a very different beast to the Little Mark heads.
I was very much of the "leave it all at noon and tweak the filters to taste" persuasion with the K1 combo, but I find the Marcus has an inherently draker tone when everything is set flat, at least through the TRV123 and STD102 cabs I have access to.
But, the minute you start tweaking it sounds amazing, with just a slight variation from straight up EQ changing the tone more dramatically than you'd expect if you are used to the Little Mark heads.
The EQ points are very well chosen (as you yourself have noted, they plug that huge gap between 800-10k on the Little Mark heads), and I really like the "Millerizer" control, as it gives a lovely sheen to the top end without ever getting harsh.
As to building up a collection of Markbass gear, I've already sold the K1: as much as I loved it, I knew this amp would work better for me. I've also listed the TRV123, but happy to hold onto that if it doesn't sell, especially since it can handle the 500 watts at 8ohms this amp puts out with ease!