I did not try Signature vs Gryphon as DAC only but did try Zen DAC vs Gryphon DAC only connected to A30 Pro. Overall Gryphon sounded somewhat better, it has better layering, Imaging and sounded a bit more refined (less distorted). It's not triple the price better, not even double the price but it is better.
Downgrading from Signature to Gryphon, I wasn't impressed by the Gryphon either, it was not bad, just wasn't as good sounding as the Signature. Gryphon or Sig for that matter, wasn't intended to be a replacement for a dedicated DAC, so most people won't be trying to pair and compare their DAC performance.
If you are primarily using IEMs, then give RU6 a try. R2R gives good body to vocals and it might be what you are looking for. If not, between Gryphon & Signature, Sig has tiny bit more body/weight to the overall sound and will drive demanding Headphone better with less hiss.