Why does bi-amping speakers sound better?

Well...  being a old house I needed some plumbing work done,  toilet swap, faucets, garbage disposal and shower controls.... I was worried a little job would become big if I did it myself.  Long story short it did still become a major job, found several leaking fitting behind drywall in not so easy places which resulted tiles are falling off around the PINK bathtub...l thus my buy amp now money is need a shower/redo bathroom money,

Bi-amping can allow some amplifiers to maintain their Class A bias longer.

@viggen900 
I feel your pain, but an old house has more character than a new one.
Hopefully, eventually, you will get to the wiring. And, as you said, it should be an easy upgrade.
 If code permits, and you can run new wiring without needing conduit, it should be a slam/dunk. I posted a thread a couple months ago regarding a whole house surge protector. If you do get around to re-wiring, I encourage you to consider adding one. They don't cost much and can give you some piece of mind, as being one layer of protection.
B

Vig, just saw this thread.  One question for you.  Have you spoken to your dealer about your situation?  It sounds to me that for the money, you may want to consider newer speakers first rather than sink money into new electronics.  Eventually doing the electrical will help, but with the new technology, speakers have come a long long way. 

I have a pair of Vandersteen Quartro's being shipped this week.  I upgraded to them in order to get an active sub built in.  The main amp will now only be responsible for sound from 100hz on up, so it frees it up greatly and will improve it's sound dynamically etc... Yes, I also bi wire.  Some designers don't are about bi wire.  This is why I try ti personally purchase 'system's' and not just randomly get a well reviewed amp, a well reviewed speaker and and a well reviewed DAC or TT.  

What is your budget?  If you sold your speakers, what would your budget be then?  It's just a thought.  Heck, my Ayre AX5/Twenty like all Ayre products has filtering built right into the unit.  I plug directly into the wall and it sounds it's best.  From the amps you mention, it all seems to be about the largest number of watts you can get, however the majority of great speakers don't need that much to sound good.  JMHO

I have Avantgarde Duo-Omega gen II, 16 ohm. I am using the Ultra-linear OTL, one stereo amplifier for each channel, full range, so no electronic crossover in the signal path. The left and right inputs on each amp is combined with a little internal wiring change to avoid using a Y connector. The right channel output goes to the bass and tweeter. The left channel goes to the midrange horn. I did it this way because the midrange horn has no crossover, so the voice coil is connected directly to the amplifier. The sound is much better than running the amps in monoblock mode with double the power driving all the speakers. In the configuration I have, the output is 20 watts per channel. With the speakers have a sensitivity of 107db, there is plenty of power. This is the reference system in my home, where I test our cable designs.