Indeed, the inboard and outboard options are different beasts. Space / layout constrains parts selection inboard. Making progress every day.
Regarding spikes . . . my knowledge is rather primitive, since all my work was long ago, before any commercial products were available, so there is plenty I don't know. I'll tell what I know. We found hearable and measureable time-domain slurring caused by recoil-swaying of the "unanchored" speaker cabinet. The woofer moves the cabinet in amounts which are very significant to tweeter frequencies, especially their transient attack/timing/phase behavior. Over many years' experience I found the presentation to be more focused with spikes. And transient tests measure more cleanly when spiked. As usual, there are other considerations. Speakers on carpet usually sound smoother, mellower . . . more polite, "nicer". I judge that mellowness to be caused by subtraction of transient detail. And another thing: direct coupling to a wooden floor can cause coupling resonances in the under-structure, euphonic-harmonic and/or dissonant, which are not stimulated with the insulating carpet or isolation-type feet. Another note is that spikes that are not locked down can absorb energy via motion losses between the threads.
There are so many particulars and mitigating circumstances that I hesitate to comment. But you asked, and my comment is that rock-solid stability at the micron scale aids the speaker in its job of transient replication.
