I've had my current amp (Image 65i) for several years and also owned other 6550/KT88 amps so have experimented before. The KT88 tube has a bit more flesh on it IMO while the 6550 is a shade more clinical, but I like both and can easily live with either.The main reason for the current switch is I lost a 6550 from old age and the tube supplier I use was out of 6550s. I've got JJ KT88s now.

I've got Spendor SP1/2Es as my main speakers.

Keep in mind that I didn't really argue one way or the other, but rather stated there was more than one way to look at the situation. What's true in your case is only something you can decide.