A couple of questions:
What specifically is it about the Blackstar tone you don't like? Could different effect pedals and different tubes change tone and would it be more cost effective than a new amp?(Not that I'm trying to discourage buying a new amp, been there, done that! ) If I remember, the Blackstar uses 12AX7's in the preamp section and EL34's in the power...What about using a lower gain value tube like a 5751*, or a 12AT7* to smooth out distortion? Also, have you or your tech checked the bias***? Just a couple of ideas to try changing tone before you buy a new amp...
*Link to 12AX7 substitution chart:
http://cydathria.com/fdm/12AX7_sub.html
***Standard disclaimer about working on an amp with lethal voltages if you don't know what yer doin', zzzap, buzzz, you're dead type stuff-seriously.***
As for me, man tone is so personal and subjective...but, the one amp that I really didn't like with either of my PRS's was a Vox AC10. There just wasn't enough headroom for decent cleans, IMO, and I wasn't crazy about the distortion either when playing a PRS. Now, I thought it sounded great with a LP or SG, but I wound up trading it for a heavily modded Blues Jr. and couldn't be happier. Like I said though, tone is so personal that I'm sure there are those running PRS's through an AC10 and loving the tone, it just wasn't for me.