What can you tell me about First Sound pre-amps?

Mphkns, Here is another hypothesis: is it possible that what you are hearing with FS on loud brass creschendo is what is sometimes called 'cuivre', or 'brassy', which can be heard live, when the metal body of the horn actually vibrates somewhat loosely under extreme FFF. If that were the case it may mean simply that FS is more revealing than other pres. But, if you do not like 'cuivre', you are not the only one. Cuivre sound is the bane of orchestras and conductors, unless it is specified explicitly in the score.

My understanding is that the OA2 tubes are either good or they are not, but they don't go bad over time. Also, as I recently discovered, the preamp works just fine even after they do go bad (or at least after one goes bad). The triode tube doesn't get properly biased is all that happens, so you may start to notice some sonic changes.

By the way, I bought 4 of them from New Sensor and it's a good thing because one of them failed pretty much right away. Apparently the failure rate is high, but if it happens, it's within a couple of days.

Guidocorona, thanks for the suggestion that this might be what I'm hearing.
I suppose it's possible. It's just that it seems unlikely that it would show up on nearly every cd in the collection, especially given that I've had some of these cds since 1991, and have never heard this particular sonic trait before, and I've had some very revealing equipment in the "good ol' days." If it only showed up on several of the CDs, I would just chalk it up to the CDs themselves, but it appears pretty frequently. The oddest trait is how it's ONLY brass that causes this effect. I suppose it's still possible that the First Sound is showing this, but over the course of 20 years, I wouldn't think that the First Sound is the first high resolution preamp to demonstrate this.
In any case, I'm more interested in doing the detective work to find out what's causing it than getting another preamp.

That was going to be my next suggestion, but TVAD beat me to it. Emmanuel will be on vacation until April 20th, after which we can ask him about the possible nepherious effect of Holco resistors on the brittle brightness of brashingly brassy brass, the moral philosophy of dual unstacked stepped attenuators, and other such esoteric matters.
In the meantime, replacing Gabrieli on modern brass with Gabrieli on sackbuts, ebony and rosewood cornettes, serpents and pendulous serpentones may alleviate your suffering and prevent all cavity fillings from shattering prematurely 'in situ'!