Powertoold,
I'm going to quote joneeboi here:
Typically the bigger the value, the better in terms of sound. A bigger value will reduce bass roll-off, but it also results in a bigger packaging. The Black Gates you mentioned will work perfectly. I actually picked up the 22uF ones, as I wanted them small as possible. The most important part, however, is the input impedance of your amp. Since you're inevitably going to be using your diyMod nano 1G with an amp, it will be helpful to know what its input impedance is. Ray Samuels amps usually have 50K input impedance, which is really great at reducing that lower corner frequency. Assuming you're using Grados at 32ohm impedance,
f = 1/(2*pi*(50,000+32)*47uf)
f = 1/(2*pi*50,032**0.000047)
f = 0.0677Hz
With 22uF caps instead,
f = 0.145Hz
There isn't too much to worry about in terms of bass rolloff, I think.
iQEM,
IMO I think the dock is a better option since you don't have to really drill anything on the iPod. If you're running to class and don't want to use the amp'ed diyMod, you canjust disconnect the dock and use the nano with the headphone out as if it wasn't even modded. You can disconnect the amp from the pigtail but you'll still have the pigtail to worry about. That's my 2 cents.