As mentioned above very strongly suggested that you wait till the audit process runs its course, because
(a) despite the verbal explanations of the auditor a to the issue at hand, once the process has started, you would want it limited to only the questioned item(s)
(b) an amended return would create a new issue -- the audit cannot be finalized till the amended return is processed and routing it to the auditor is error prone -- thus there will be two parallel line items in your account -- will just delay the resolution
(c) it is extremely unwise and dangerous to volunteer information that has been requested or under review --- note that once the auditor determines there is an error in one year, you would wnat that kept bounded to that issue and hopefully to that year -- by offering to amend implies that you knew you were at fault or it is willfull disregard of the law and so on and so forth -- they can then go check all the past years --- there is NO sunset for fraud or willfull dis-regard.
(d) also you don't know for sure whether this is just a pure line-item complaince review or something bigger -- let them open the kimono and show their deck of cards
(e) if you have filed as honestly as you could have, there is nothing to be afraid of -- just "steady as she goes". And if it turns out that you took shortcuts, then deal with that problem when that is proven -- show that it is was an error ( fickle finger, understanding or ??) and not disregard for law. Granted they will track you for a few years to make sure that you have become compliant
Good Luck
