Lack of depth problem

they all roll off around 1 Khz - well before a dome tweeter can take over

What I meant to say is that the horizontal dispersion rolls off. (this is caused by beaming)

Another way round this is to use cones that flex allowing the centre part of the cone to decouple from the outer edge - this is called controlled breakup and you can see it on some woofers with "rings" although you do not have to have rings to exploit cone flexure - it has drawbacks in temrms of added distortion and an uneven frequency response.

I had a similar problem. I had given up and concluded that my speakers were incapable of producing depth. On a lark I purchased a DIY power cable from VH-Audio - Flavor 4 with the Furutech connectors. I wasn't looking for a fix here, just curiosity and was hopeful for even greater spatial cues and detail. After inserting said power cable everything changed. My speakers took on a character they NEVER possessed. This was especially true in soundstage depth. Just a thought..

I don't think you need tube traps on the ceiling, Vett. I just like to experiment, having had tube traps since 1988 and still find them great for absorbing bass.
If you have any "jogs" in the room, bass does tend to pile up there. That jog in my room from 13' to 12'8" was piling up quite a bit, something I didn't realize for many, many months. Otherwise, just a couple in whichever corners you can put them in should smooth out any humps in the bass. It's also helpful (but only it it's not overly expensive) to have a height of 6' on the traps, which means 2 of them. I have found that the closer to the ceiling you get, the more the sound improves. I put a box in between my bottom and top trap just to see if it improved,and it seems that higher up is better! You can always try the Real Traps, but it sounds as though you have enough damping for higher frequencies, which are, as I recall, pretty short. I think a 1khz wave is 1" long -- or shorter, so I wouldn't worry about that too much. One could have a tall ficus tree to break up those wavelengths. It's the upper bass that I find haunts most rooms of normal size.

Speaking of bass: depending on where those subwoofers are in relation to the mains- a time shift can screw up your sound stage also. There's a lot a ambience info in the bottom octaves. Try moving them into alignment with the mains as an experiment.

The coupling caps in the NP100 are Jensen oil caps and have been there for 6 months. So I think they should have broken in already. V-caps do take a long time to break in. I have a pair of V-caps in my 300B SET amp and they took 400 hours to break in. The first 200 hours were simply horrible....

I'll test my other tube amp over the weekend. One subwoofer is at an right angle to a speaker. I'll adjust it too and see (or hear) how it sounds.

I'll also keep moving the speakers forward and increasing the toe in.

The power cord for my NP100 is already a VH Flavor-4 PC! It is a fine power cord. It replaced a Shunyata Copperhead PC, which rolled off on the highs. Maybe I should put it back as a PEQ that Shadorne suggested?

This high-end audio hobby is expensive but interesting. There are so many things to learn! I built my first radio more than 30 years ago and built many amps as a teenager. At that time, I played violin, guitar, and trumpet. So I have pretty good ears for music. Then I went to college and got all my degrees in EE. But I am still learning many new things. Thanks everyone for sharing your experiences.