The most discouraging thing ever was plugging the Altec 511 horns in for the first time (they were scavenged from the Astrodome, RIP). They sounded like a squawky nightmare. I ended up doing some unconventional crossover settings and that helped -- but the main thing was to only power them with about 18 tube watts each. They really sorted themselves out then.
To me the big difference between vintage analog gear and modern stuff is that modern stuff usually sounds "good" right out of the box. But if you take the time to dial the old hi-quality stuff in, you end up with something really special.