I own a specialized industrial equipment manufacturing company which I started 20+ years ago and has done quite well. Our sales and growth have stagnated over the past few years primarily which I think is due to : #1. Being 'home-grown', we have lacked professional marketing/sales and have primarily depended on referrals, online (Google etc.) marketing & a few print ads in trade magazines. #2. Over the past few years I have spent lesser and lesser time at the company with zero efforts towards new marketing channels etc. Recently we were approached by a very talented individual who operates (CEO) a similar but unrelated niche manufacturing company. I believe he could take our company to the next level as he has done at his existing company. Of course no guarantees but I am willing to set aside the considerable cost associated with this endeavor for a year or longer, assuming I see some ROI within a year. Which brings me the to the question above!
My suggestion is to structure his role to be clearer more senior in terms of responsibility so it is not a direct comparison of unequal pay for the work (if confidential salary details leak through employee discussion). Also, if employees make a decision to exit based on salary alone, an organization has bigger issues to grapple with. Employees decide to stay more for culture and leadership quality than any other factor. So, if this fella is as good as you think he is, think it will be the best investment for everybody at the company who can benefit from his coaching and mentorship.