Notice the two ch power delivered is not half of the one. Nor is the five ch 1/5th.
2ch total power 244w. 5ch 375w. 4 would be slightly less, but more total than 2.
OK. Let's assume we are discussing something like an Emotiva UPA-5 which has a normal cost of $550. And I'll assume that 4-channel manages just as much total power (374w) (-1 so I can divide more easily).
That means 187w per channel from bi-amping with a multi-channel amp.
Well... not really.
See, what that actually means is 94w per channel into 4 channels (two HF, two LF)
So here comes that spike we were worried about clipping, and it's a thump at 110w at 80Hz on the right side. On our non-bi-amped, we didn't clip (remember, 122w per speaker), but now that's trying to run through just one channel (right low-frequency), and that (according to your measurments) is 94w or so.
And the story gets worse from there. We could have, instead, spent about the same money (yes, the UPA-5 is an oddball this month cause it's on sale... I'm skipping that because it's anyomolous) to get an XPA-3 and had 200w per channel to handle that spike. That's not only more power than the real power available to a single driver (94w) that's more power than the theoretical power for a spike with absolutley even dispersion between HF and LF (122w)... and by a lot.
Maybe we should bi-amp with two amps? It gets *much* worse then. Two UPA-2s will put you out $700. You get a theoretical 250w per channle, but only 125w per driver... and you've buttedup against the price of an XPA-2 which has 300w per channel.
I don't want to get too stuck on Emotiva. Perhaps you'd like to use Yamaha ProAmps (what I have here at home). $419 will get you a 250W amp, times 2 and you'll be out $838.
500W Yammy pro? $629.
Even if we make the case that bi-amping 2x250 offered an advantage over 1x250, it certaily is not advantageous over 1x500, which is also cheaper.