Soundstage Confusion

I'm in the midst of choosing a new amp for my listening room. Currently, I'm using a NAD M22v2. I just auditioned at home the LTA power amps, and really like their ZTOL40 Reference amp. I also have my faithful Pioneer SPEC-4 that I've had for over 35 years. My components:

Herron VTSP 3A(r02) pre amp
Innous Zenith MKII media streamer
Small Green Computer i7 Roon for DSP device
Audio Mirror Tubadour III SE DAC
Technics SL-1200G TT
Parasound JC3jr phone pre
Tannoy DC8Ti speakers

My room is 13.5x11.5x8.  I've positioned the speakers 34" from the back wall and 22" from the side walls. I've been futzing with speaker placement and my listening position for a while. I have no room treatment yet.

With the NAD and my current setup, I get a huge soundstage and room filling sound. The speakers disappear, but imaging is awful where voices and instruments are well forward of and outside the speakers, with little depth. With the ZTOL40, and no other changes, the main voices are centered between the speakers; instrument separation is clear and overall imaging is great; the soundstage is between the speakers; and the speakers do NOT disappear.  

To test soundstage and imaging, I'm using Chesky Records Jazz Sampler & Audiophile Test files that I downloaded from HDTracks.com, in particular track 10 Introduction and Left-Right Imaging Test, track 11 Listening Environment Diagnostic Recording, and track 12 Acoustic Soundstage (depth) Test. The ZTOL40 passes all tests with flying colors. The NAD fails them all.  I moved the NAD to my rec room system in place of the Pioneer amp. Soundstage is between the speaker; imaging is OK, and voices are centered.  Later today, I'm going to hookup the Pioneer amp to my main system and run the Chesky tests.  That should be interesting.

Before all of this craziness started, I had a different rack.  This past week, I replaced it with a Butcher Block 4 shelf rack. Before that rack, my speaker and sitting positions were slightly different; the NAD soundstage was between the speakers; and imaging was fine.  With all other things being equal, I'm finding it hard to believe that a different rack and/or an amplifier change could cause such a drastic change in soundstage and imaging.  Any ideas anyone?