Tip o' the week - Jamming along with pre-recorded music
Most two-channel amps will work amazingly well as a way to play along with pre-recorded music. With the right adapter, a computer, CD player, Ipod. etc. will sound pretty good when plugged in to the same input as a guitar or mic would use. Use the lowest-gain input if you have a choice.
Of course, your harp mic will be plugged in to the other channel, and you will be able to mix the volume to match the music.
Sure, it's a compromise, but it really sounds like you are "in the band" when its all coming out of the same speaker. Try it!
Skip Simmons