I assume he/she is telling you to enter into a mutual agreement wherein both parties drop all claims against each other and take nothing. However, you have to be careful in these agreements and make sure you cover all the bases. It might cost you a little, but I suggest you have a consumer lawyer look at this, at least any agreement. See www.ConsumerLawyerHelp.com
At a minimum you should request a mutual dismissal with prejudice to avoid a subsequent lawsuit.
Better would be a Mutual General Release in addition to the above.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
If you have attorney's fees, you must have an attorney. If you have an attorney, the collector should direct all communications to your attorney, not to you.
"Mutual walkaway" is an ambiguous phrase. IF there is a lawsuit on file, they would need to dismiss the lawsuit "with prejudice", meaning that they cannot file another lawsuit later. Are they asking you to release any possible claims, or even unknown claims, that you may have against them? Are they going to report the settlement to the IRS as "income" upon which you must pay taxes, using Form 1099-C?
It would help if you met with an attorney to review the specifics of your situation.