I think PowerAMP is the most powerful one with lots of options and wouldn't be surprised to see it supporting those volume keys.
I'm wondering about 4GB limit too, hoping there is a workaround or maybe custom ROMs will solve it. Most of my files are 4-9GB in size.
But as long as I'm in range of my network, DicePlayer plays them brilliantly over the network, I use ES File Explorer to map my LAN drives.
For players that are not able to play from networked drives, the solution is to use CIFSManager which mounts networked drives as a local subfolder, fooling player apps into thinking they are playing local files. DicePlayer doesn't need that workaround.
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