Good question! Ask Phonak to publish the technical specs on their DSPs and maybe we could begin to find an answer. Unfortunately, the biggest players in the hearing aid market are very secretive about the details of their products. They are perfectly happy to sell them for outrageous prices to desperate people who think they are getting something better.
Many of us on this forum have called for head to head comparisons of hearing aids but they have been slow to emerge. Consumer Reports did publish a report in July, 2009 - the first timid step toward getting comparative information. Specific HA details are here but you have to have a subscription to read them.
IMO, the next best way to estimate hearing aid quality is to look at the capabilities of their components. Most of us do that automatically, when buying computers, HDTVs, etc.
Well, the most important component in today’s digital HAs is the DSP - the computer that processes sound and adjusts it to compensate for the wearer’s specific hearing loss.
The DSP, with a microphone and a tiny speaker, fundamentally, constitutes a hearing aid. So, it seems to me that the DSP is the most important component to look at.
So, try to get a technical Data Sheet from Phonak! I’d love to start comparing them on the basis of their performance features - and - what they actually cost to produce.