Biamping, yes or no?

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.

"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."

No offence at all, but I disagree. The preamp is so vital to good sound, you would be far better off upgrading to whatever you can get for 2x the price of the W4S, instead of buying 2 of them. Same thing for the amp. I think you would have much better results if you just upgraded to 1 really good stereo amp or a pair of mono's. There are a lot of technical issues you have to deal with when you biamp. For example, you will almost certainly need to get an active xover. Just putting something like that into your system can do more damage to sound quality than the extra amp(s) can provide from the biamp in the first place.

"For example, you will almost certainly need to get an active xover. Just putting something like that into your system can do more damage to sound quality than the extra amp(s) can provide from the biamp in the first place."

But, generally, passive XOs have a more deleterious effect that active XOs.