I've heard dCS directly to amps with glorious results [ie feeding Wavac, Graaf, Conrad Johnson, Audio Note] and very bad results driving Lamm or some other ss amps.
Basically if you do not use preamp you'll have to pay attention to system balance, cables and everything else.
I spent quite some time to find a preamp which do not harm the signal, not loose speed and sound transparent and if addding a bit of harmonic richness in the end.
And basically a tube-preamp adds space (ambience?) and spatial information which directly you can't have it this way. A ss preamp should be world class to outperform dCS direct.
In general I've found that if you use tube amp dCS direct is the way to go -in most occasions [lamm needs its preamp]
when you use ss amps a near-world class tube preamp cann add the above spatial info and air and not harm the overall sound.
Of course all this with system matching, top cables, good equipment decoupling and speaker-room compatibillity.
In other words there's no free lunch and easy sound; system matching is above all.
For the fun I remember a guy who got amazed how dCS Puccini "killed" his cj preamp, and I was amazed in another system listening dCS Elgar-Verdi-Purcell driving directly Graaf200 and SF Stradivaris there was no need for preamp in those occasions!
On the other hand I also noticed that with dCS gear you can have it both-ways. What I mean is that you can hear jazz, small classical, voices with preamp and Rock, orchestras directly for that immediate slamm and energy (but less 3D).
IMHO.