The Matter Condenser shows the negative int limit and does not store any energy.

This would appear to be an issue on AE2's end.

For now, just use a 64k at most for the matter condenser. Anything above that — especially a 256M — is just wasteful.

Just a follow up, 64M is working perfectly and it actually works to store excess energy by setting to destroy items than to matter ball/singularity (where 64 item singularity + 256000energy is the max if singularity is set), it can instantly convert to 64 singularity/matter ball by just deducting the corresponding energy from the storage.