x264 and x65 from ffmpeg are advantageous in double pass encoding. In single pass, you already have software/native encoding in Resolve, which I consider equivalent in speed/performance.
As far as I know only single pass is available in Voukoder yet, for SDK constraints. If you want double pass x264/x265, you may export to DNxHD in Resolve and double-pass with ffmpeg/Handbrake later.
2 pass encoding is basically analyze how much quantization compression per frame (x264), or per block/unit (x265) in pass1, then in pass2 encoder adjust the quantization compression level more evenly. So overall you still get lower quality (and slower) than CRF mode (constant rate factor, 1 pass), if you give a higher bitrate in pass2, then you defeat the purpose of 2 pass, so at least in video production/editing phase, it's not recommended to use 2 pass at all 