I can't hear a difference. That doesn't mean someone else can't. It does mean that the difference may be subtle. I also know that I could mic up a genuine Soldano SLO, post a video on Youtube saying it's a VST and I'll get a dozen comments saying "doesn't sound like the real thing". Regardless of the reality of tubes, it sounds like this tech is rather opinionated & very pushy with his opinions. While he may be an outstanding tech, he's crap at customer service. I imagine being so opinionated causes a lot of unnecessary conflict with customers. I would pass on grumpy tech & look for someone who understands that the "customer is always right".