Welcome to the world of gain and sensitivity. Tube amps and preamps can have deceivingly high gains. This doesn't mean that they're more powerful than a solid state amp with lower gain!!
Remember that most tube circuits were designed when sources were analog, and extra gain was useful. And lots of popular small-signal tube types have gobs of gain on tap. So it's easy to make tube gear that has tons of gain.
But now we're in a digital world, where balanced DACs commonly push out 4V signals. The high gain preamps and power amps are no longer needed, or maybe even desired. So a lot of more modern SS designs forgo the extra gain stages. This means it can be difficult to even "max out" some SS amps when you're using an analog source. Meanwhile, a high sensitivity tube amp is easy to "max out" because it has simultaneously a lot of gain and not a lot of power reserves!
In short - your Legacy amp is probably fine. It was designed with lower gain on purpose.