To my ears, Monqiue is fairly dark sounding tube gear compared with REDDI, Noble or some other Tube amps/gears. I currently own and used to own some of them, depends on the style of music and how dense is the mix, Monique may sound muddy in some situations compared with other Tube or clean preamps especially for an IEM mix you're talking. (Not a Monique/power amp/speaker combo), because power amp section and speaker / tweeter still contribute some sort of EQ/tone to it.
For a DB751, I considered that as clean tube sounding gear already, so you may find it without any problem for most cases like what you expreienced with the Noble preamp, because they both got some sort of tube warmth while there is enough top end in it plus you can add more high if you wanted.
So it is all depends on how your instrument naturally sound, if your instrument is relatively warm sounding with less attack like a traditional Alder/indian or Indonesian Rosewood combo in most cases, you may find the bass sound too mellow or dark with Monique in many mixes, not bad for some music but definiltey not good for all.
For an IEM bass mix, like 90+% of my working situation is IEM gig, you may find surprisingly you actually need more top end on the bass in order to cut through and sound more presense, so Monique may not work on a Coppolo sometimes, or you can try to boost the high on the Monique all the way up and boost the Coppolo's high as well, and you will see what I mean.
so I won't say that's a problem or a bad thing for a Monique, they just sound like that way and it is a tonal option out there.
