I have the same configuration (Generic Software on Realtek HD Audio) on 64bit Vista and my 'Max' is set to 64 - also without me ever touching that setting.
I tried to find something about the capabilities of the realtek audio codecs and drivers concerning polyphony but without success.
My guess has always been that 32 simultaneous voices should be possible but I've got no clue as to where the limiting factor is located in this mashup of hardware, windows, drivers and lotro.
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