Adding tube sound to my SS system

I suggest the OP could use a few more direct thoughts on what he experienced, which was that a switch in preamps provided engaging midrange but a lack of bass and soundstage...perhaps that means HF detail to pinpoint stereo image?

Keep in mind this may have nothing to do with tubes at all. Much of the sound quality of a component system comes from the relationship and synergy of the components.  

This is nowhere more true than the match between preamp and amp.  Impedance, how hot the signal is...very relevant stuff.  

Additionally, if the OP always has loudness on with his preamp, then either (1) he isn't actually that fond of its sound or (2) he listens at low volumes.

My suggestion:  try different preamps until you get an amp match (or I suppose vice versa - but I'm presuming the amp and speakers are a good match to eliminate variables). 

For example - you use the Lumin to control volume...try that directly to the power amp.  Not my jam -- I have found I strongly prefer an actual active preamp in my system -- but it is worth it to get a sense of what needs effort. 

See if you can borrow a couple other preamps. Or do the math and find one that matches the power amp. 

Finally, I have found that tube buffers are a bit more of a novelty than anything else - one thing to actual use tubes in the necessary circuitry, but a tube buffer really cannot do more than coloration.  At least the ones I am aware of - perhaps some help with component matching or similar (in which case put it b/w the pre- and the power amp). 

My bottom line is that being somewhat analytical about upgrade paths is going to help you get to your objectives faster than just pulling out the wallet or taking gear recommendations from posters with different systems, different rooms, and different ears. 

To me, matching gear is at least equally important to some perceived "gear quality" based on price or similar factors. Secondarily, people are constantly surprised at how toe-in (or not) on speakers, and adjusting front and rear feet on them, can make a massive difference. 

I don't have the space for a full tube preamp. But a tube buffer is another matter. In my big desktop system (SS headphone amp/preamp [Violectric V281], class D amps [Bel Canto 600Ms], speakers [Harbeth 30.1s] and sub [JLAudio e110], I use a DAC that combines old-school Philips chips + a tube output buffer: the MHDT Labs Orchid. I have the best NOS buffer tube plus adapter that I could find.

The results are subtle and all positive. There is obviously real synergy in this collection of components. When I switch in a "better," more expensive NOS DAC, the Metrum Onyx, the sound via speakers is not quite the same. Yet in a different, headphone-only system also using the Violectric V281, the Only easily betters the Orchid.

(synergy)

A few years ago I had a Musical Fidelity tube buffer stage that you could put between pre amp and amp or into a tape loop, etc.  I personally did not care for it, but it or something similar may be an easy easy and inexpensive way to add a little tube sound into your current set up.  Got rid of my Mac tube amplifiers also.  Guess I'm a SS guy all the way.

Reporting back after a ton of research and experimenting. 

I've been demoing the LTA Aero and Mojo Mystique Y in my system this last week and thought I'd share my early impressions.  While waiting about a month for these to arrive, I also tried some other speaker cables.  Supra 3.4, Mogami w3104, Oyaide Tunami v2, and Neotech 3001.  I had some excessive brightness/harsh treble that made some tracks hard to listen to.  Speaker cables made a huge difference surprisingly and each of those upgrades provided noticeable improvements! 

System now is Roon Nuc - Ifi Zen Stream w/ elite LPS - DAC - Luxman l509x - Spendor D9.2.

I previously had a Lumin T2.  I don't think it synergized well with the spendor Ds and luxman.  It was too detailed and analytical for me for speakers which already lean a touch that direction for my tastes.  

Both of these DACs completely changed the system for me.  Albums I previously thought were poor recordings revealed by my revealing system are now enjoyable.  There is more weight, organic richness, tone and life to the music.  I could happily live with either one.  Its going to be difficult to decide.

I swapped tubes in the Aero to the Ray Tubes Reserve 6sn7.  That changed the character of the Aero and made me realize how tube rolling can influence the sound.  The 6sn7 toned down some of the incisive zippy nature of the Aero and gave more tonal richness, lifelike insight into the music.  I've also been trying a Cary SLP-05 tube preamp into the separates input on the luxman which is pure magic.  The Aero with stock tubes straight into the Luxman gave perhaps 30% of the tube magic vs including the Cary in the chain. The Ray Tubes Reserve 6sn7 gets me 70% of the tube magic while retaining more of the drive and solidity of the Luxman preamp.  The aero with the 6sn7s into the luxman I would describe as spacious, detailed, insightful, organic, rich, airy and alive.  The band sounds in my room vs listening to a great recording.  Acoustic and jazz shines.

The Mojo also sounds fantastic and swapping back and forth between the Aero and also including the Cary preamp it's difficult to nail down a clear winner.  The Mojo is smooth, dense, very composed and clear.  The soundstage is a touch narrower but more dense.  It is even handed.  It also has similar giddieup to the Aero with the 6sn7 tubes (although not as much as the stock tubes which want to boogie).  I seemed to like the Mojo best relative in comparison to the Aero with more produced music like Abbey Road or an Eryka Badu album. 

At this point I'm leaning towards the Aero with the upgraded tubes and sticking with the Luxman vs going tube pre / ss power amp.  It gives me some of the tube magic while keeping the setup simpler and it sounds fantastic.  Its a tough call though, the Mojo also is a lovely DAC.  The Cary is special.  I have more listening to do.  Thanks to all the folks on this forum sharing their experience.  Really happy with how things are sounding over here.