Wyred amps and Merlin VSM-MXe speakers

Anyone using this combo? I know the Wyred amps are engineered to work well with tubed preamps (which I currently use). I tried the STI-500 integrated but noted a bit of harshness with an Eva Cassidy song that wasn't present with my Belles 150 Reference amp and Bel Canto SEP-2 (tubed) preamp. So I'm wondering if the harshness may have been coming from the pre section of the STI-500, and thinking this may be ameliorated by my tube preamp.
Use the HT bypass feature on the wyred integrated and you by-pass the built in pre-amp all together. You can use any pre-amp you wish with the amp section only to evaluate your problem.
I wouldn't call the STI harsh at all. Is it brand new and maybe needs to be broken in? What are you using for a source, cables, etc...? Is the room treated?
In my experience, many of Eva Cassidy's recordings are harsh sounding... even when I had a tube preamp going into OTL amps and electrostatic speakers. So maybe the Wyred is letting you hear how those recordings actually sound... It is a very revealing amp, though not a harsh sounding amp unless the recording is actually harsh.
Sorry - I should have mentioned I no longer have the STI-500 integrated. I currently am using my long time Belles Ref 150 Reference amp with my Bel Canto SEP-2 preamp. I just purchased a ST-250 power amp and will compare it this week with the Belles. Eva's "Over the Rainbow" was the song I was referring to, and it has never sounded harsh over my current amp setup.