Is bi amping worth it ?

601 mono-blocks, that’s supper over kill for K-horns. I would not bother trying to bi-amp with that much power available. Unless you're considering moving to low power amps then maybe splitting the mid-tweeter and bass would help. That said if you’re not getting punchy bass from your K-horns I’d look at set up issue and speaker location room interaction first.

From my experience with Klipsch speakers (LaScala’s in my case) you’re better off with lower power amps, you are never using more than a few watts at best with 105bd speakers. I ran mine on 2.5watt SETs, 8wpc SET’s and some really nice 25wpc SS class A amps, and it was glorious. 600wpc is so over kill you’re barely getting that amp out of idle no reason to add more power IMO.

Subwoofers are hard to match to K-Horns but it’s possible with good quality sealed units. I would think that’s a better direction if you wanted more bass, after you address any set up issues and room interactions. You do have them in corners, right?

Unless you live in 1950, no.

No, it really was not worth it in the end. 

Tried it several times and a few ways, with the same of each amp. Vertical and horizontal configs. It could sound "exciting" at first, but never convinced me to stick that way for longn. Seemed less musically coherent somehow (there can be slight differences in units of even the same model of an amp). Not good results with bridging SS amps to mono, either. What I didn't try is biamping with disparate amps (like tubes up top) - but honestly the coherence issue when biamping with the same SS amp turned me off that idea.

What CAN make a big positive difference is taking two stereo tube amps that can be switched (paralleled) into mono, and running them as monos. 

This was done with Tannoys that are relatively efficient. 

Three ways to improve your base I can think of...

1. Call Greg at Volti Audio and ask about upgrading your driver and/or crossovers.

2. If you're streaming music, get a streamer that has EQ.  I use Eversolo w/o using their DACS - just straight stream, but their EQ in their app is easy and excellent.

3. Dual quality subs that have crossover adjustment.

I integrated a pair of REL Carbon Specials w/ my Volti Rivals (using McIntosh C2700 tube pre w/MC462)... Set crossover fairly high so mid-range voice comes through.  Is unbelievably good.  Adding well integrated subs improves presence, warmth, makes the soundstage wider and deeper, and when you get it right adds a rich holographic overtone.

But Klipsch bass driver loose/flabby - would clean that up first, then think of next step.  Call Greg.