I recently did a Tango session with a Bandoneon recorded close mic'ed in a concert hall. Not that these instruments are the same, but there are similar issues. Generally you will need at least two microphones. I would stick with the same types, ie. Ribbons or Condensers for bass and treble. Keep in mind that the accordion moves in and out, therefore technically causing a phase shift between the mics everytime that thing plays. Solution might be to use a small diaphragm capsule extension that is fixed to the instrument with a contraption to keep the distance constant - i.e. the mic moves with the instrument (Schoeps or MBHO makes them, but I guess these are not part of your arsenal). I would go with clean preamps with high gain for the Ribbons - the Syteks or Great Rivers. I have had great results with some Beyer Ribbons and the Syteks, but for this session I believe I used my small diaphragm AudioUpgrades-altered AKG 460Bs. I do not own the Great Rivers. If you want a more "athmospheric" sound, perhaps a simple ORTF or XY pair in front of the player would do the trick - this will depend on the recording environment and aesthetic (as always). If you don't need isolation and want a low bass sound try some omni on the bass to mix in. I would be curious to hear about your results - please post!!
Cheers
