"and knowledge that you appear to be infringing"
This is what I'm trying to wrap my head around. What defines "infringing"? The patent abstract covers some features that we do, but also some that we don't.
How much overlap is required before it's considered infringement?
Whether you are infringing depends on how the patent claims are drafted. That I cannot tell you because I can't give legal advice.
If you want to learn for yourself before going to a patent attorney, pick up a law school textbook and start reading. The law isn't hard. You just need to understand how the courts have interpreted the Patent Act.
I used this one in law school (used copy will be fine): http://www.amazon.com/Intellectual-Property-Trademark-Copyri...
Get the supplement, too (supplement gives you the recent updates to the law): http://www.amazon.com/Intellectual-Property-Materials-Supple...
They are in Portland, they are IP experts.
Your best bet is to ask around at the Chamber of Commerce or other business meetups near you.
You have knowledge of an existing patent and knowledge that you appear to be infringing.
Again, you need a lawyer. Get an IP attorney.