Biamping, yes or no?

The chances of doing something like that and having it sound good is almost 0. If you want to upgrade, why not just go with the M180's by themselves? That would probably sound a lot better.

Two pairs.

you'll need to add an active crossover to get real benefits of biamping.

You might get a second W4S STP/SE preamp, and use one preamp each for left and right channels. Use the balance control on the preamps to fine-tune the balance of low and high pass. Use one stereo amp each for left and right channels. You'd have to use Y-splitters on interconnects from sources to preamps.

I've never done this, but I imagine the Tyler D1 speakers would like it. Make sure to use star-grounding to avoid ground loop. Also, if using a power regenerator, connect line-level sources and preamps, but not amps, to the regenerator.