I just recapped my Infinity RS6's and for me a warm sound was achieved with bypassed Sprague caps on the tweeters and small Vit. Q bypass caps on the 2 midrange caps.
What could have and has been before, an edgy, forward, shouty sound all of a sudden became 3 drivers fused as one with a "just right" crystal clean high that made EMIT's famous (and me love them ever since the mid 1970's) and 3" Polydome midrange that has every opportunity to stridently bore a hole through metal if not done right.
Now it's mellow, but not sappy, recessed mellow, and brings out even more detail than before.
This was not case with Solen PP caps without a 0.47 PIO bypass to take the harsh out.
Now if only the old Luxman was still working it would be the ideal combination I've waited 30's years to rediscover.
Now, old Luxman gear, that's a whole 'nother chapter in "mellow". Same for Marantz.
Both have their own chapters that redefined Mellow as having it all there, never fatiguing, yet never leaving out the detail, soundstage and dynamics you expect.
Both, and many more manufactures, are famous for a "Mellow" sound that's frankly, addictive, and allows you to listen to it without fatigue for hours at a time, especially with a good TT setup.
Older Pioneers could be called "Mellow" too I think, The SX-626, 828 etc lineup, but when you get into the 950-1010+ late 70's kit, I wouldn;t call it mellow. Certainly excellent sounding, but a harder sound. Lots of power, but missing the "echo" an ;aid back sound of the earlier models.
"What is Mellow?" is a great question to ask on the AK.
It really is a relevant question to the amps, speakers, cartridges and even DAC chips in CD player choices we all use here.