I too use an iPad for MANY things - including music playing. Using unrealBook for charts/sheets works perfectly for me. What I find is that there is a dilemma in that there are SO many good music-related apps (virtual instruments, MIDI control apps, even vocal processing apps) ... that I'd need 2-3 iPads to do all the things I'd like to do!
I have an iPad 3 and keep my old iPad 1, and I usually have both of them on my keyboard rack, one for reading music, and the other for various things like using OSC for MIDI controls, or to use a virtual instrument, etc.
I was thinking of exploring the ik multimedia iRig PRE for a mic, and using their VocAlive app - but I'd need yet another iPad (or iPhone) to dedicate to that! :-)
Perhaps I need to buy up a few old iPad 2's or similar 'cheap' ...
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Genos / Tyros5 / HK Lucas Nano 600 / FTB Maxx 40a / EV ZX1A / Rock'n'Roller cart / Hauptwerk virtual pipe organ / misc other audio & music toys