Woah :S :hap5:
1. An amplifier does what it's supposed to, that being AMPLIFY the output signal for speaker systems that are connected to the same.So audio quality originating from your phone will remain the same but will sound louder,richer etc. according to the output device.
2. AFAIK,both have a music software that manages your phone's tracks and are quite straightforward to use.I haven't personally used them so I suggest you wait for more inputs on that or look up reviews on the same.
3.
Music playback file formats: .mp3 AAC, eAAC, eAAC+, MP3, Midi, WMA, WAMR, MXMF
4. & 5. It has been verified that the 5130 supports mem. cards upto 16GB !
So if a device supports such capacities,there won't be a problem.It does of course take time to browse through the tracks(plenty of them) but that's a no brainer.
6. If there isn't a setting to increase brightness then I'm afraid no 3rd party app. can help you achieve the same.
Hope this answers everything.
~ T.T.M ~