I don't need a bigger amp for my set-up but when I've listened to different amps with the same speakers, I've noticed a difference in SQ when played at the same volume. I guess what I don't understand is why bi-amping is different than simply getting a more powerful amp.
You could get more power, but only with the right speakers.
Lets take a three way with a crossover between woofer and band pass at 400 Hz. This is the acoustic power divide. Lets assume the terminals when the jumpers are removed go the low pass filter, on the bass which powers the woofer. Then the other set of terminals will go to the band pass and high pass filters. Remember filters are in parallel with each other, until you remove the jumpers, then they are isolated.
Lets assume that the music program is pretty evenly split either side of the power divide.
As long as the amps can maintain full power at the same time, then you will have doubled the power and gained a small 3 db in output. It will not sound twice as loud.
Now if the program switches for a moment to where there is a lot of content below 400 Hz and much less above 400 HZ, a common scenario, then the bass amp my clip and the HF amp will sit idly by and not be able to come to the aid of the LF amp. This is why an amp twice the power is less likely to clip, than two amps biamping.
Now lets take the more usual situation these days of a two, or two and a half way speaker with a crossover to tweeter around 2.5 kHz. The exact number is not important as it will be well above the power divide at 400 Hz.
Now when you remove the jumpers, the lower terminals supply the woofer and the upper terminals just the tweeter.
Now the bass amp is delivering practically all the power. The amp to the high pass filter, supplying the tweeter provide relatively a minute amount of power. When the bass amps clip the HF amps can do nothing to help. The HF amp will deliver an insignificant amount of power.
You will not get a measurable increase in spl. As far as HF and LF current in wires is concerned, I really doubt this has any effect, and if it does, is way below the threshold of being audible.
So you see, in the situation of most speakers discussed on these forums, you get absolutely no benefit from biamping. To get a benefit you need to be able to access a set of filters with a crossover point between 350 and 500 Hz. That restricts you to three ways, with a woofer/band pass crossover accessible. And by the way, I have seen a number of three ways where the accessible filters are the LF/band pass on the lower terminal and the high pass on the upper. This does not help you one bit if you are contemplating passive biamping.