The ZROCK seems to have been designed primarily to go between source (DAC,etc) and pre-amp but can certainly be used between pre and amp.

I have the ZROCK2 (not 3) and find I can only really use it between the source and pre-amp in my Decware system. Chain = Streamer/DAC > ZBIT > ZROCK2 > CSP3 > UFO25.
When the gain is set just right across the whole chain, I get a really full and enhanced sound. I tend to get a slight buzz when I push the gain too far (which doesn't happen too often at all) and only can be heard between tracks or quiet passages. Again, with my current gain settings across the board I hardly if ever hear it. My Zrock has the full Anniversary mods since I wanted it to keep up with the UFO25 and CSP3 which has full A-mods as well. In my case the Zrock's knob is set to around the 12:30 - 1 o'clock postion. That's all I really need when my DAC is connected. I use a little more when the TT is connected. (FWIW)

If I place the ZROCK2 between CSP3 and UFO25 I get a buzz no matter how I structure the gain. I tried this because I wanted to use both my DAC and TT through the CSP3 without changing IC's. I can't use it this way and since I use the DAC most of the time I don't mind connecting the TT to the Zrock when needed. (my component layout makes it easy to do)

Since you seem to only have one source, connecting the ZROCK3 between source and pre should work great for you.

Input impedance of pre and amp is certainly a consideration and definitely follow up with KHOZMO or Steve for a definitive answer. However, I have read in other threads that the Zrock can possibly work with impedances as low as 10k (someone please correct me if I'm wrong) but almost always seems to be system dependent. Obviously, the higher the better but may work fine in your application. Again, Steve would know better.

If the impedances work out with your system (which is very nice by the way) you should definitely try it both ways. Can't hurt and then you can see where the synergy lies.

The ZROCK2 was a great addition to my system and I think it will be what you're looking for. Here's hoping it all works out and good luck!

The figure I got back from Khozmo concerning the input impedance of my passive preamp:

"It varies from 0R (mute) to 500K (max)"

I'll contact Steve eventually and go over the details.

Then the ZROCK3 would be OK between the preamp and the amp (with my current setup)?

Would replacing the Khozmo preamp with a ZBOX work?

DAC >> ZROCK3 >> ZBOX >> Amp

OR

DAC >> ZBOX >> ZROCK3 >> Amp