You don’t need to be afraid of the NX5. We have three and use them daily. The problem we discussed in this thread is the only problem we have had in over one year of use. It seems isolated. In fact when I searched for threads discussing the same problem, this is the only one I could find.
When the cameras were released I read about a lot of people having problems with (1)backfocus (2) problems with recording to the HXRFMU128 optional 128-GB Flash Memory Unit. We never saw a problem with the backfocus and believe it was a problem with early units. The memory problem was quickly solved (apparently) by a software upgrade. I can’t comment because we don’t own the 128 – gb memory units.
But for your application
-low light
-music recording
-amateur
-small camera
the nx5 or ag-ac-160 may not be the best choice.
To our surprise, we are using the Panasonic Lumix GH2 for situations as you describe. Equip it with the standard 14-140 lens and also buy the 20mm 1.7 pancake lens. In low light the little 20mm pancake lens will give you unbelievable footage. Even on automatic. This camera package is under $2,000. To shoot what you are describing we would put one on a tripod and carry another. Yes, it is a photo camera. Yes I am suggesting you use it to shoot the video. The reason this is a better choice is simply that the sensor is so much bigger than a $4,000 video camera. In my opinion, in low light the GH2 photo camera has a huge advantage.
To me, the sound is a bigger issue. It is a band. To me the sound quality is more important than the video. I think you will find that none of the cameras mentioned will give you the sound you are looking for. I would buy one or maybe two Zoom H4 audio recorders. They could be placed near the band members using the internal mics and/or with professional microphones. Multiple audio tracks of the band will have a richer and far more professional sound. The Zoom recorders are about $300 each.
An audio engineer on another thread who we respect wrote that anybody that didn’t own a handheld recorder was stupid. We were stupid. We immediately bought two. Now we use them all the time.