It was in Park but was it in Ready mode or simply IGN on?
The 12v battery really doesn't have much in reserve (it only has to boot the computers and power the entry system) so I always put the car into Ready mode if I'm 'playing' with settings etc.. Definitely when just parked up listening to music whilst Mrs Nemesis spends the money...
The ML audio is streets ahead of the standard offering (I've had both versions, first RC was the pre-facelift) but I don't recall finding an equaliser setting menu. Just finding the fader is a faff..