Best channels for reaching CTOs and Heads of Engineering at mid-market companies?

We sell an on-premise AI platform to engineering leaders at companies with 200-5000 employees. Our ICP is very specific - they have large legacy codebases and can't use cloud-based tools due to security restrictions.

LinkedIn outbound has been our main channel but response rates are dropping. We've tried content marketing (blog posts, Linkedin, Youtube) but it's hard to rank for terms our buyers search for.
What channels have worked for you when selling to technical leadership? Reddit, developer communities, and meetups are full of developers - our end users.
But in our case, the deal is usually decided by a buying committee: CTO, VP Engineering, Head of Platform, Security, sometimes even CFO.

Budget is limited - we're a small team of 6.

Would love to hear what's actually driven pipeline for others selling to this audience.