Nice, but there are two essential things missing: keyboard expression [1] and polyphony [2].
[1] http://en.wikipedia.org/wiki/Keyboard_expression
[2] http://en.wikipedia.org/wiki/Polyphony_and_monophony_in_inst...
[1] http://en.wikipedia.org/wiki/Keyboard_expression
[2] http://en.wikipedia.org/wiki/Polyphony_and_monophony_in_inst...
For key velocity (is that what you mean by instrument expression?) -- there's maybe not much point attempting to tackle that when it's not emulating instrument voices yet anyway, or supporting MIDI input. You can't exactly capture key velocity from a computer keyboard.
There's some mention of gain in the code snippets, at any rate -- I think each voice may have its own "volume knob", in effect -- but I haven't dug into it at all.
I think that's a limitation of your keyboard. Here I can play zxcvbn, but I can't add a seventh note.
USB keyboards are limited to 6-key rollover. Using a PS/2 connector will fix that.
http://www.reddit.com/r/hardware/comments/nydvp/why_does_usb...
http://www.microsoft.com/appliedsciences/antighostingexplain...