For example, the Steinway Grand has a bit too much reverb. Can I reduce that? I don’t see an obvious way to do it.
There’s a reverb knob on the on-screen MIDI keyboard that you can open from the View menu. Alternatively you can open the n-Track Sampler properties and the reverb setting is the last in the (long) list of parameters: click on the box + arrow icon in the left side of the track to open the track’s instrument plugin, then tap on the gear icon in the upper right and select “Show generic user interface”, then scroll all the way down to show the reverb slider. Or you can set the reverb amount using MIDI control change 91.