Hi Harry

A single stereo pair can cover a full symphony orchestra given the right mic type, location and, and pairing technique. The built in mics in something like a Zoom like unit (I prefer the Sony PCM D50 but that's just me!) are usually cardioids in a so-called X -Y pattern. Width/eveness of coverage is up to the sound guy (you!) and how the mics are placed. Hint - nowhere near the camera.

"Hint - No Where near thr camera" made me laugh!! True that!!

So short of buying every type of mic. If you were to have only two mics that could be used to mic a two party interview or mic an orchestra, which two mics would you get? Wired XLR balanced that is

The requirements for a 2 person sit-down interview and for stereo recording of an orchestra are so different that finding a single pair of mics that would do both jobs well would be out of the question, IMHO. For the sit-downs, a pair of Tram TR-50 omni lavs or perhaps a pair of the new Rode lavs would be a good choice. For recording the orchestra, a pair of small diaphram cardioid condensors such as the Rode NT5 or Audio Technica 2021 or 4021 would be worth considering. (Brands mentioned only as examples, lots of others would fit the bill.)

Take a look at the Sony PCM D-50 if you haven't already - its built in mics are rather good at the price - it might be good enough for band/orchestra. I use mine as backup for almost everything I do. Certainly not as good as my regular setup, but considering the 10 -20 X price difference I'm extremely happy with it. And sound quality is really quite good. It has really excellent limiters for this class of device.

You could probbaly get intelligible voice with it as well, but I think Steve's suggestions re lavs is a good one

I use a couple of small pocket recorders with my lavs - I use MicroTraks which are not much beloved by a lot of people here, but I've been satisfied enough with them for the occasional use I make of them.

You might be able to run two lavs into the Sony via a Y cable - haven't tried it myself so might be off base.