I was amazed how the sound changed when I got my new bow, which is quality carbon bow with black hair. Many recommended here black hair and sticky rosin for Spirocores and so I choose Pop`s rosin and black hair. Many consider Spirocores beeing scratchy and difficult under the bow, or even unbowable, but still there are some amazing arco players like Terry Plumeri and Renaud Garcia Fons, who use exclusively Spirocores and some major orchestra ( can`t remember which ) section uses Spiro solos tuned down etc. It`s said a lot here too that the scratchiness is more audible to the player than it is to the audience.
I`m no expert and am not aiming to be an orchestral player but still I believe it`s about what you learn to live with and what kind of sound you`re aiming at. I love Terry Plumeri`s Spirocore sound and bowed guts -type of sound. I don`t mind them beeing scratchy, thats part of the magic and I might get that woodwind / voice -kind of sound and that rough and powerful kind of folk / solo jazz sound, if I shed obsessively enough

I have a gut G over Velvet Animas now and I`m waiting for a used set of Gamut guts to arrive. Same bow and same rosin, although I have dryer Petz rosin too. If fresh Spiros are scratchy let alone plain gut, no matter which rosin or hair on the bow. Like someone here said, it`s not the strings sounding scratchy, it`s you sounding scratchy. Go figure...
Hope that you find a solution to your problem!
Reiska