Why does bi-amping speakers sound better?

I am 90% sure which brand of amp I want to get, just trying to figure out if I should bi amp or not.

as a example should I go with

two 2 channel amps at 400w x 2 so each speaker would get 400x2

or should I go with a single 800w stereo amp so each speaker sees the same 800w, just with one channel of a amp

According to this datasheet the "power rating" of the Kappa 8.1 is up to 300 watts. So an 800 watt amplifier would presumably be overkill, as would two 400 watt amplifier channels per speaker. Also, I’ve read that the 8.1 is not quite as current hungry as the Kappa 8 or Kappa 9, which if I recall correctly have notoriously low impedances in the bass region.

Given that, as well as the 6 ohm nominal impedance of the speaker, it seems to me that the best and most cost effective approach in this particular case is likely to be a single stereo amplifier having an 8 ohm power rating in the area of 300 to 400 watts, and a 4 ohm power rating of double those numbers or close to it.

Keep in mind that part of your amplification dollars goes toward watts, and part goes toward sound quality. Therefore paying for watts that won’t or can’t be used may misdirect some of those dollars.

But to answer your more general question:

In the case of passive biamping (i.e., without an electronic crossover "ahead" of the power amps) the main benefit that can potentially result in most circumstances is that each amp channel will only have to supply current and power in part of the frequency range. Which eases the burden on the amp, and can potentially improve its sonics. Also, in the case of vertical biamping (i.e., assigning one stereo amplifier to each speaker) the sonic effects of inter-channel crosstalk that may occur within the amp, if any, are presumably eliminated since both channels of the amp are provided with the same signal.

In the case of active biamping (with an electronic crossover "ahead" of the power amps) each amp channel will only have to supply current, power, and voltage in part of the frequency range. Which can provide further sonic benefits, increase flexibility in choosing amplifiers, and make it possible (although not necessarily practical) to eliminate the speaker’s internal crossover.

Biamping is a more complex undertaking than a lot of people realize, however, and can in many circumstances do more sonic harm than good. Especially if non-identical amplifiers are used.

Good luck. Regards,
-- Al

I've not found that biamping works all that well but there are a ton of variables.

Two of them are amplifier quality and speaker quality.

A third is the quality of the crossover- which is certainly one of the more important variables!

Now the amps I play at home can go to 2Hz with full power, and yet do mids and highs quite well (they are tube amps after all). My speakers go to 20Hz so I run the amps full range. I find that quite often a poor electronic crossover means that you can't get the speakers to blend and often you loose detail (since the crossover is an additional block between the source and amplifiers). I've experienced this a number of times (and used some pretty high end crossovers).

So- success is based on extreme care! If the crossover is designed for the specific speaker used I think you will have greater success.

Perhaps monoblocks would be a better option than bi-amping? Two matching amps, driving each speaker has major improvements over a single stereo amp. Due to each having its own power supply, greater separation, and generally they are the better amps a company makes. 

When bi-amping, you've got to be careful with amp matching. If you run two amps of the same size, the bass could seem weak. If you run a larger amp on the bottom, the bass could be too strong. So, careful matching is required to be sure each half of your speaker is running at the same SPL. When you drive a speaker with one amp, the amp sees the speaker as one load, the designers have designed the crossover to level them out, to keep top and bottom at the same level.  But if each amp is seeing a different load, they can react differently, causing your sound to be too much bass, or too much treble. 

There are speakers built for bi and tri amping, with a crossover that comes before the amps, or active crossover.  So each amp only has to work with the frequencies of the speaker it is driving. And can give fantastic performance, but amp selection is highly critical. And the active crossovers usually have a volume control to help with balancing. 

Bi-amping can give amazing results! But, it can also cost a lot of money, and cause a ton of headaches trying to balance the system. Since money is always a factor, all of your money invested in one amp and one set of wires can be more cost effective than halving your monies to buy half as good amps and half as good wires. Assuming we get what we pay for. Can two $3,000 amps sound as good as one $6,000 amp? Can two $400 speaker wires sound as good as one $800 wire? Debatable. 

the bass could only seem weak if the amp runs out of power - and that is less likely when bi-amping

monoblocks & bi-amping both are expensive as pointed out above - you need more transformers for the power supply

one driver, one amp is the ultimate design - you just have to create a cost- and SQ- effective realization

not that amps are a major determinant of SQ compared to speakers, room and source recordings anyway

Thanks for the input/options everyone... it has helped however I still can't decide :)

i am actually leaning towrds trying a class d amp from d sonic.  Debating mono block, stereo or multi channel.  I did visit a local audio shop yesterday, they mentioned they had a NAD 5 channel class D amp at $4k, Anthem 5 channel A/B at $5k and a McIntosh 7 channel A/B at $6,500.  I mentioned/asked about multi channel vs stereo/monoblock and his response was since I use a AVR (Integra DHC 80.3) that I wouldn't see any benefit from mono blocks or a 2 channel amp.  If I didn't use a AVR then yes monoblock or 2 Chanel amp is much better.  

I am leaning towards trying class D due to moving into a old home, built 1865 thus not the best electrically in the place.  I worry that if I go with and amp that's A/B that it wouldn't get the juice it needs.  One of these days when money is willing I will run 1-2 20A service to where the stereo stuff is but that's going to be a while.  

Yes, my 8.1's are rated around 300w, however for a really long time I have been one who likes having more power then less power.  I prefer my ears say no well before the amp or speakers say that's to loud! For whatever the reason I have always thought it just sounds better that way feeding more power.  I also hope to get a better old infinity speaker at some point.  Possibly just the kappa 9.1's or their renaissance 80/90 or preferably something from the IRS line.  Thus trying to think ahead so whatever I buy now will have enough oomph to power whatever I get next... which will be a few years down the road.