I found this article for you:
When sound is amplified to match your hearing loss the number of bands and channels determines how closely the amplification matches your loss. Imagine it like a stereo system. Some have just a tone control, some have a bass and treble control, some have a 4 band graphic equalizer etc. It’s all about manipulating the sound to match your loss.
The problem is that its not really about how many bands or channels you have, it’s about how it sounds to you. The article I showed you shows that once you get above four channels there is little further improvement to be had. The problem in comparing these figures from one manufacturer to another is that they all have subtly different meaning. One manufacturer may produce an aid that has eight bands, but if those bands are not truly independent, it may not sound any better than another kind of aid that has four bands.
If you look at this link you can see a bewildering selection of hearing aids, some expressed in bands, others in channels, other in both channels and bands. But this data is largely meaningless. I don’t think even a professional could draw any real comparisons based on this information.
All that said, you probably want at least four channels. But don’t fall into the trap of assuming that if it has 20 channels it must be a better sound quality. This is not necessarily true.
What you should be concerned about is whether your hearing professional can demonstrate good hearing to you by means of letting you listen to some real digital hearing aids.