I think that it’s more of a question of How can I NOT play more than one instrument?!
I’m primarily a flutist, but I pursue harp as a side instrument. And then there’s piano, and the dozens of ethnic/folk flutes that I play…
In terms of balancing them all out though, I have found that they really balance each other. Piano and harp really help my sight reading on the rest (reading music vertically instead of horizontally), and my technique on flute has to be MUCH faster than technique on harp (for my music preferences at least), so it helps with speed of finger placement.
When I play, I guess I think more about ideas and concepts rather than specifics. I think about how things span the gap between the instruments. When I roll chords I think about them as if they are fast arpeggios on flute and that they must be clear and even (and vice versa). When I think about internal resonance when playing flute I think about how my harp vibrates and how it feels.
In all honesty I find my various pursuits to be very gratifying. They all express something that the others cannot. I am looking forward to a gig I have coming up this summer. I’m going to be doing a regular series of performances at a Renaissance Faire nearby. I’m going to be performing on celtic flutes/whistles, lever harp, and will be teaching about the instruments. Considering that the Renaissance Faire is supposed to be set in 14th Century Scotland, I’m really looking forward to teaching audiences about my flutes, and our beloved harps! I get to blend all of my interests into one performance series. Yay!
Oops… sorry. Tangent at the end!