Speaker mash up ?

Oh Boy!

You would be best off using the full Magnepan speaker, and adding some sort of other speaker as a 'cheap' subwoofer (really a low midrange, upper bass boost)
But yeah, not that it is great, but certainly some folks would enjoy it.
A few posts of folks using multiple sets of loudspeakers and loving it.
We each have our own wants.
Purists would complain, but who actually cares?

My experience is that instead of accentuating the virtues of each you bring forward the bad side of both. The way you propose to do it will be very bad if I understand it properly as the crossover point will be god knows where and how will you achieve the right sound balance between the speakers. Are you using an electronic crossover with level controls? Can you do it? Sure. Should you do it? I wouldn't do it but it is your money.

I had a bud who ran a pair of pre outs to two different amps hooked up to two different pairs of speakers and all playing at the same time. All mid-fi mass produced stuff. I'll tell you what- there was nothing missing! Okay so it could definitely sound congested and confusing sometimes but his music collection and knowledge far outshone any deficiencies in his system.