I use Ableton Live's inbult "Convert x to MIDI" (with x being your choice of Melody, harmony and rhythm) to do this. It's not perfect, especially if there are effects that create harmonics/Overtones/resonances on the source materiel ie: distortion and reverb, but you can pick through the MIDI data and tidy it up to get what you want from it. I use it fairly often when sampling other people's stuff to create complimentary sounds etc
Also, as DRodriguez said above, you could look into Melodyne. The newest version handles polyphony extremely well. If like you say it's less of a pad and more of just a note based texture, it should pretty much nail it. Also, despite being primarily marketed as a "pitch correction" tool, It's also a mad tool for repitching and fucking shit up, if that's something you are interested in.
Neither option is particularly cheap if you don't already own them however.