The answer is still "it's streamed." Can you mute samples in a WAV file? The closest you'd be able to get to sample muting is a setting like "mute from 1:32 to 1:33." That is, 1 sample of music is equal to a specific amount of time in a song. Because it's streamed, it accesses the samples sequentially. It runs through these samples very very fast. For example, in a 48 kHz file, there's 48000 samples per second. If you were to mute any of them, then instead of removing a specific "instrument" or whatever, you'd end up with silence in that area.
If instead you want a "play *ONLY* the samples between 1:22 and 1:24" then you can do that easily enough in a WAV editor. In other words, I don't think a feature like that is applicable for in_cube or VGMstream, or whatever. To my knowledge, there's no other Winamp plugins that can do that either. Mouser X over and out.