Tube change.

I agree with Bgross. I'm guessing that you have a pair of VTL 225 amplifiers. I have a VTL ST150 so it may use the same tubes as your's. If your amps take  6350 drivers make sure that they are still strong and balanced. There's not much to be gained in rolling this tube since they were all made by Sylvania as far as I know but the triodes need to be balanced to sound their best. The 12AT7 tube contributes most of the character of the amp. My favorite 12AT7 type input tube for the amp is a Brimar 4033. It, along with a Mullard 12AT7 are wonderful in the V1 position but I think that the Brimar has a significant edge in body and drive, especially when in Triode mode. Also, try playing (within reason) with bias to fine-tune the sound of the amps to your taste as they will respond well to changes of a few millivolts. If one or two tubes stray from their bias setting by 6 or 8 mV you will sense that something is off.  For the longest time I ran my amp in tetrode but after replacing the drivers it sounded fantastic in triode mode and I can't switch back.

My apologies if you don't have a VTL !

Over the years, I have owned several "high end" tube-based amplifiers. With one exception, they have all been designed or optimized to run KT88's. Subsequently, I have spent a ton of money "rolling power tubes" as well as signal tubes. Currently, my tastes have taken me in a TOTALLY differently direction. Being a former classical musician, I strive to achieve the most realistic and musical reproduction from my system. 

To be quite frank with you, the KT88 tube has never quite satisfied my tastes, regardless of the amplifier in which they were used. I have tried almost every brand, including some very expensive NOS tubes. I have also tried CRYO treatment on several. All the results have been less than satisfying to me.

Now, you mention SOPHIA ELECTRIC. That is one company that I have not tried, though I have read several professional reviews and reports, which highly praise the SOPHIA ELECTRIC products. Especially, the EL34 and the KT88 as preforming at a much superior and musical level as anything else out there.

Eight SOPHIA matched tubes is a pretty big investment chunk.

Also, I have no idea what the rest of your system is comprised of. 

I would only caution, depending on your musical tastes, that the end result might not be as dynamic as you would like to anticipate. ESPECIALLY if your tastes run toward Heavy Metal, Rock, and the like. "CICO"!!

Using the SOPHIA tubes "MAY" yield subtle or more sophisticated improvements. All of which tend to be more evident if you tastes run in the direction of classical, jazz, or small ensemble music. 

SOMETHING TO THINK ABOUT.!

@jbsqg I have the Triangleart TA-350m mono’s. 8 Kt-88 tubes(can’t use 6550) 3- 6ns7 tubes driver 1-6sl7 rectifier tube. I was told the power tubes on the amps would make the biggest impact on sound quality. SE of course makes no guarantee but states customers report a significant improvement in almost every area musicality, soundstage, bass, midrange when using their tubes. Even though expensive considering it because it’s still less than upgrading to another amp and less hassle than trying to sell mines. I’m very pleased with my amp but this little voice inside me keeps saying What If?

@axpert I have the Triangleart mono’s mentioned above.

Triangleart L-200Mk 2 preamp + Rhea power conditioner 

Emm labs transport and dac, Trenner&Friedl Isis speakers