Has anybody here done this?

The following was taken from (audo video revolution); it's part of a review that they have done on the Sunfire.

Randy Bingham at Sunfire urged me to try a second Sunfire Signature Amp in a vertical bi-wire configuration. This means you use two Sunfire Signature Amps. Each is fed an unbalanced signal to the normal input then the lab input for left and right are bridged with a single (mono) interconnect. If you bi-wire or tri-wire your speakers as in the case of my reference Cello Stradivari Legends, you should connect the high/mid leads to the current output while using the voltage output for the bass leads. Got it? Good. Don't worry it took me a minute to figure out too.

The best way I can describe the change in sound is to make a car analogy. I drive a six-cylinder VW GTI. It meets my budget and my need for speed which is a nice tradeoff. The difference a second Sunfire Signature Amp made is like trading in your GTI in on a Porsche 911. The extra power elevates the music to a whole other emotional level. Yes, I know there is an extra $3000 plus an interconnect included in the price of this upgrade, however it is worth it. And who said you ever had to buy it all at once?

The sound of the vertical bi-wired Sunfire Signature Amps multiplied everything good about the sound of the amps. The best test for the effect of the second amp was using the new MCA remasters of Jimi Hendrix's Axis Bold as Love. On "Little Wing," Jimi's guitar floated in space, something I have heard in few systems. The power of these amps was frightening. I don't believe in inefficient loudspeakers. I like my Cello's, WATT's and Puppies and even slightly less efficient transducers like THIELs and Martin Logans, yet these Sunfire Signature Amps feel like they can drive any difficult load from Apogee Grands to a Lincoln Town Car.

I wonder if anybody here has done this and if so, did you find it to be worthy? Thanks.
Not sure I follow your explanation since I don't have a Sunfire amp, but vertical biwiring is not new. Its typically described as using two stereo amps, one to drive each channel. Either a y-adapter is required at the amp, or if you have two main outs from your pre, the left outs go to one amp and the right outs drive the other. Then the speaker outs from one channel of each amp drives the woofer and the speaker outs from the other amp drives the mid/tweets. It can be very good in the right rig, providing a big improvement in separation and imaging, as well as current delivery.
Yes...vertical bi-amping can make a very big difference sonically. Glad you heard the improvement.

But..what you should have done is get the VW 1.8T engine and put a larger turbo and cross pipe with a ecu chip and cat-back from APR performance and you would be smokin with 297 bhp/ 290 Ft/Lb torque like me! My Jetta likes 350Z's! :)
I am currently running a vertical bi-amp configuration now. I am getting great results, but I think it is a bit of overkill in my situation. I am running Infinity Renaissance 90 speakers, and one Sunfire Signature would be more than enough for a pair of those. I just happen to have 2 of the amps from my old setup when I was running the Kappa 9 speakers.

My concern in doing a vertical bi-wire and running each amp in bridged mode is....what happens to the amp when you run speakers with a nominal 4 ohm load that dip to 1 ohm like the Infinity Kappa 9? Can the bridged amp handle the strain when presented with a 1 ohm load?

I ran my Kappa 9 in bi-amp mode and got great results.

I understand bridged amps can run into trouble when impedances drop, so I stayed away from the vertical bi-wire bridged setup because the impedances dropped so low on the Kappa 9.