Znak -
Thanks for responding to me up above; I haven't had a chance to write you a decent response before now.
By "tube rolling", I mean trying different tubes to get the overall sonic characteristics you want. "Rolling the front end" would mean trying different tubes in the front end, in hopes of enhancing the overall synergy. It's kinda fun.
I appreciate your articulating the requirement for "differentiation of instrumental timbres". I've never heard that expression before, but it's richly descriptive - I'm gonna remember it.
Differentiation of instrumental timbres would be facilitated by natural decay of the notes, so that the harmonic structure isn't blurred or colored. Any resonances will spoil the timbre as the notes decay, because the ear perceives a sound that lasts longer as being louder.
As a side note, when Jon Dahlquist designed the legendary DQ-10, he had to choose between aligning the leading edges of the notes, or the trailing edges of the notes (attack or decay). His listening tests indicated that the ear is more sensitive to what's happening in the trailing edges of the notes, so that's what he optimized in the DQ-10.
Loudspeakers that don't use boxes have an inherent advantage in getting timbre and decay right, because at least three potentially significant problems are neatly sidestepped: internal box resonances, box panel resonances, and re-radiation of the woofer's backwave through the cone. As an example of this breed, the Quad 57 is still celebrated for its clarity and natural timbre.
If you want full-range reproduction with extremely natural instrumental timbre and decay of the notes, there are three speaker lines I suggest: Audio Artistry, Beveridge, and Sound Lab. Audio Artistry uses dynamic drivers and gives you more of a front-of-the-hall presentation; Beveridge gives you more of a middle to rear of the hall presentation; and Sound Lab gives you more of a middle of the hall presentation. I'm a dealer for Sound Lab, but still an admirer of Beveridge (see www.beveridge-audio.com) and Audio Artistry. The two electrostats mentioned here give you a very wide sweet spot, and while the Audio Artistry line gives a more conventional sweet spot, their dynamic impact is phenomenal.
I'm not saying that these three are the only possible solutions - only that they excel in the area you have highlighted; namely, differentiation of instrumental timbres. "Full-range" single-driver systems like the Beauhorn also excel at this, but don't have authority in the bottom two octaves.
I can talk your ear off about either the Beveridges, Audio Artistrys, or Sound Labs, if you'd like to know more.
Best of luck in your quest,
Duke