I don’t have any direct experience in this sector, but I’d encourage you to start by better understanding the segments of your market. Whether through interviews, surveys, or product usage analysis (ideally some combination), you’ll need to identify the common threads between segments of your seemingly-fragmented base, and then create personas based on those segments. Some dimensions to consider that span across job titles/industries/buyer types: “jobs to be done” (see Clayton Christensen’s work), decision criteria, substitutes, level of pain, willingness to pay, etc.
Disclaimer - I've never marketed to this segment.
That said, I find it very hard to believe that you can't pick our four or five comon archetypes among your buyers. You're solving a few common problems. What are those? How are you solving their problems? Go out and talk to 20, 30, 50 customers. If you can't pick out four or five common patterns among your buyers, you might want to consider whether this is a market you even want to be in.
I think the biggest mistakes with starting a formal VOC program are 1) to do it without truly knowing what the goal is, and 2) to not secure CEO-level buy-in. If you don’t do the first one, then how will you know where to focus or how to measure the impact? And second, if you don’t get that commitment from the CEO, then you risk turning it into a temporary pet project that ends as soon as the exec sponsor departs the organization. I’ve seen it happen first-hand.
Hi - yes - I definitely recommend sharebird's resources. I also love a few books on positioning. First the classic book here is from Al Ries and Jack Trout and it's called "Positioning: The Battle for your Mind." I also recommend "Obviously Awesome: How to Nail Product Positioning so Customers Get It, Buy It, Love It" by April Dunford
Have a strong point of view on the market and don't be afraid to reframe the current definition, but be prepared to invest heavily in education and thought leadership. Rely on proof points to support your narrative in the form of customer advocates that evangelize your definition and why it drives value. The good and the bad news is that someone has already created the initial interest - invest in execution and authority marketing to grab market share.