Mark was kind enough to send me 2 of the fuse boxes to try on my preamp and power amp. I'll do my best to give my impressions, though I feel like the sound is still changing and improving.
Out of the box (copper sluggo):
Bass. More in both quantity and definition. I considered dialing my subwoofers back a few times in the first hours, but eventually decided it sounded 'right' with my original setting.
I'm noticeably lower on my line stage's volume control. Maybe 5 steps lower (out of 103 total). I usually listen around 30 and am now listening in the mid 20s.
Instrument separation is better and the leading edges of notes are more clearly defined.
Soundstage depth is reduced slightly. Soundstage width is unchanged but the outer edges of the stage are more illuminated.
Complicated passages are congested.
Vocals and high frequencies sound a little etched and somewhat artificial like I'm trading some naturalness for additional detail.
After a week (approx 25 hours):
Soundstage depth is back to where it was. Improvements in width and illumination remain.
Congestion on complicated passages is no longer an issue.
The etched quality I noticed initially has settled down nicely and things are sounding natural again.
I like what I'm hearing.
Today:
I have lent the fuse boxes to a friend of mine for a couple of days to try on some other equipment.
Before I removed them from my system, I briefly tried the brass sluggo. I think it is the better sounding choice for my system. Tonality and texture on stringed instruments seems appreciably better. High frequencies seem more natural and appropriately scaled. I'm less confident in these observations because they were made in about a half hour but will follow up when I have had more time to compare.
Last night, I listened without the fuse boxes in my system. It was a short session, not as engaging. I'm looking forward to continued experimentation with the brass sluggos.
I'd also like to try polishing the sluggos and treating them with progold or bullfrog contact enhancer.