Soundstage depth how to improve? Shootout

It's loudspeakers and amp, you already have it figured out. 

Try before you buy to check for any parameter that is important.

Can't shoot until receipt of FOID.

Your setup similar to me, I also have Coincident Statement MKII and custom build 300B monoblocks, extreme modded Klipschorn. My ss pretty much like yours, most recordings  balance of sound just behind front baffle of speaker. But this sounds extremely natural to me, plenty of image dimensionality and image layering, images just closer to me than I've heard in some systems. Klipshcorns and required placement certainly have something to do with this.

I also have Coincident 845, had Prima Luna Dialogue Four, have used Denafrips Hyperion, Musical Fidelity M2si with Klipschorns. Also have Merlin VSM-MM, again with extreme mods, used these with two different 845 SET. Also Joule Electra LA100MkIII, Schitt Saga+ pres, and finally dac direct with number of dacs. In all cases my ss has been centered just behind front baffles of both speakers. This would suggest my room and room treatments dictating ss to large effect vs. equipment.

With Merlins I could manipulate ss depth to larger extent, I used room treatments, toe in, speaker placement. Ultimately, I prefer more forward, ss,  I've had previous systems where ss more recessed, just didn't have the immediacy and extension into room I prefer. I've even gone to using various room treatments with intent to extend ss into room, I go for sound immersion.

SS placement doesn't matter that much to me as long as I have image dimensionality, images are what supplies the depth. I prefer the performers closer to me.

It also may be true DHT and SET  have inherently more forward SS, I've heard this mentioned by others. Certainly part of what I hear as immediacy in these tubes.