Is bi amping worth it ?

FWIW, the big advantage to passive bi-amping is being able to match amplifiers to speaker requirements.  In other words, you can run a big honking amp to power your power hungry woofers to bring out their capabilities and use an amp that you love for it's midrange and high frequencies to power the mids and tweets.

If you vertically bi-amp you are using identical amplifiers on both highs and lows (oftimes a stereo amp).  This can work well if you are somewhat compromised in power requirements in the first place.  It also allows for short speaker cable runs and maybe more convenient placing of the amplifiers.

In your case, I wouldn't use a second pair of 601s for the mids and highs because your speakers are efficient and you would only be using a fraction of their power.  A much smaller amplifier would work just fine and possibly be much less $ than a second pair of 601s.

The biggest issue when using different amplifiers for the highs and lows is matching the outputs.  In my case I had to tame down the bass to match the highs, by using an attenuator between the preamp and the monoblocks.

As always, YMMV.

Bill

@wbs 

It makes sense to me for the OP to do what you are doing. It would require an additional stereo amp but I think it would serve him well. 

In my situation, I use two equal stereo amps. One drives the bass portion of the AR9's and sits two feet from the right speaker. The other amp sits two feet from the left speaker. I have 4 eight foot cables as I believe I should keep equal lengths. I don't see your point of allowing for shorter cables in my situation. I do when someone uses a mono amp right by the speaker that it drives though. It seems to be a fairly common practice and allows for very short high end speaker cable and much longer balanced cables from preamp to amps. 

other Bill:)

@billpete 

Hi other Bill

I was just pointing out that if two identical stereo amplifiers are used, one channel of each amp could drive the woofers and the other channel could drive the mids and highs.  Configured in this way each speaker could have it's dedicated stereo amplifier positioned near the speaker.  And, it would be a lighter load on the amp's power supply than if both channels were driving woofers.

The comment about shorter cables is mostly esthetics.  Personally, differing speaker cable lengths don't bother me.

Bill 

@wbs

I'm having trouble wrapping my head around that. In stereo, wouldn't this mean that I have one channel driving the bass and the other channel driving the mids/highs? Isn't this kind of defeating "stereo"?

Interesting thought about the length of cable. I know that electrons flow at the speed of light (at least I think they do) so maybe it would be impossible to actually "hear" a difference in minimal length differences. I was more thinking of there being ever so slight differences in the resistance which maybe could affect it in some miniscule way. With all these tweaks, we start splitting hairs and claims of perceived differences become a source of much speculation some outrageous discussion. As long as I like it more than before is really all that matters to me and I do read a lot here for the opinions of the fine folks here who have a helluva lot more money tied up in a system than I could ever hope to have. 

@billpete 

I’m having trouble wrapping my head around that. In stereo, wouldn’t this mean that I have one channel driving the bass and the other channel driving the mids/highs? Isn’t this kind of defeating "stereo"?

No.  "Stereo" is in the source, then gets split to be amplified by right and left channels.  You still have distinct left and right channels in the system.   It might be easier to think of them as two separate 2 channel amps rather than two stereo amps.