One of the more vexing of questions for the engineering side of me is how come active preamps sound better than passive ones.
Take the StellarGold preamplifier. Here's an active device that in every case helps the system sound remarkably better than without it. Compare that to a passive volume control or stepped attenuator, or just simply a DAC (like its mate, the StellarGold DAC or MKII DAC) directly into a power amplifier.
Insert the active preamp and magic happens: more space, better dynamics, more harmonic richness, more you-are-there.
How does this happen and why?
I wish I had a great answer, but I don't. Here's a few tidbits of what I do know.
The average preamplifier is actually worse than no preamp. This became apparent to me years ago when this whole thread began and I inserted between the DAC and amplifier, the Aesthetix Calypso preamp. Boom! Magic. That revelation led me down the path of designing our own versions: the BHK Signature and now the StellarGold.
Extended high frequency response matters. One thing in common with all these active preamps is their ability to extend the frequency respond out well beyond human hearing—50kHz and beyonds. In a passive preamp we find the combos rolling off much earlier.
Those are just a few of the noodlings I've been working on in my head.
Perhaps others have ideas to chime in?