So the bug fix of OBS studio 28 has been released. As mentioned in a post about the beta version, OBS provides support for AMD's AMF encoder on all GPUs that support the AMF encoder.
This video incudes how to enable B-frames on 6000+ GPUs. Included are a couple other settings you can use to optimize your hardware encoding on all cards with AMF.
That being said, still pondering an Intel A380 as a second GPU to use as an A1 encoder, but waiting for RDNA3 features to see if AV1 hardware encode / decode support is included in the new cards. Built a new system around a 5900X last August, but have a 3 year old non ray tracing card as I've been waiting for prices to drop.
AMD Encoder Optimization Guide - OBS Studio 28 link: