The old Delta DC that I found last year had terrible bag filter (I doubt that it even had a micron rating) so I bought a canister filter on Amazon. Much cheaper than the Wynn but still has a MERV 15 rating. The prices seem to have have increased a little recently but are still cheaper than a comparable Wynn filter. This is the one that I bought to fit my smaller 1HP DC but they have a larger one that will work better for larger DCs. Another option is Donaldson filters that are also Merv 15 rated. Shipwright did a write up on another website a while back about using them to upgrade his HF DC .
The biggest problem I had getting this DC setup was sealing the clear collection bag on the bottom. The bag clamp allows enough air to leak out that it was spewing a little dust into the air. The solution was to use some of the narrow stretch wrap found with the moving and packing supplies at HD. A couple of tight wraps around the top of the bag and clamp sealed it up. It will be easy to just wrap again when I empty the bag. I keep the stretch wrap in the shop to help clamp awkward shaped glue ups.
Speaking of canister filters and dust collection in general. I stumbled upon this YouTube video that used a canister filter and an inline blower for a air cleaner. The the air cleaner is at 1:18 but there are some other tips in the video that might be helpful for some.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.