I have a 3203 Artist. Just got last summer.
It is about the best sounding Marshall amp head that I own. Even though it only is using one preamp tube to flavor the preamp, the tone
I get from the Artist is nice, fat and buttery.
It sounds as good as my Jubilee, JCM DSL 100. It comes in above my DSL40 and Origins.
Seems to me when the Marshall guys that started Blackstar, used the design format of the Artist to create the Blackstar tube amp line.
Not sure why you are not getting a full tone from it. When correct, it should sound awesome. I think the guy taking about dirty jacks or other may be on to something.
ONE THING ABOUT MY ARTIST, the loop jacks seem goofy. I have to keep a short guitar cable connected to the loop plugs for mine to play.
Check that area.
Congrats on the 3203 and cabs, glad to see you went out and got it. Seems like the 1966 cabs are a little harded to find so scoring two is pretty awesome.
Honestly I should play mine more. I was in a variety band the past two years and needed a huge variety of tones so I was using a mfx board, the Marshall wasn't quite compatible. Hopefully I can get w/ some guys this year and wind it up outside the house. Even though it doesn't have pre-amp tubes I think the clean channel sounds pretty damn good clean and also when you get that master turned up and the volume up around 6 it's nice power tube over drive. Of course, the lead channel smokes. I had more fun with my 3203 w/ attenuator. get those power tubes working.
If it's sounding thin run it with the Master vol turned up around 8, that'll fatten it up some. I've got a 1965a that I'm keeping stock but for my 1966 cab I have a Greenback and V-Type I'm going to put in, I don't think the G12T-75s are do that amp any favors.
Got it all cleaned and put back together...sounds awesome! FWIW, I use an EH Metal Muff in front. I'm seriously impressed with the tone and that was just a test with my Ibanez S420...can't wait to hear what it sounds like with my Les Paul.