Answer to an inquiry from Germany – related to Unison Simply Italy:

6CA7-Z and KT88-Z were released over 10 years ago to the market as the very first high end upgrade tubes. But over years, the factory’s lack of quality screening has flooded market with mixed quality. We (Grant Fidelity) no longer carry them as the ‘selection’ cost is simply too high and performance varies too much. 

WE Plus series is the latest release before Shuguang factory went into relocation and ceased production in 2020 till further notice. From our own evaluation, the sound of this series is much better than previous Z-series (yes people do hear lots of good things about Z-series as they have been on market for 12 years with certainly more users). We selected through the entire factory stock and acquired less than 10 quads which meet our quality standard. We won’t hesitate to recommend them, simply just by the excellent test results we have seen on those we picked.

For your amp – i see the manufacturer website showing it uses EL34. It can be replaced with WE6CA7Plus no problem. I don’t see mentioning this amp can use KT88 – so please make sure your amp indeed can use KT88. If so, WEKT88Plus can be used. 

In general, KT88 gives more bass low frequency but resolution for midrange and high frequency isn’t as good as 6CA7. You can have to decide what is more important to your listening and choose accordingly. 

Hope this helps.