First Watt Sit-3 paired with Klipsch Cornwall lV?

If your Cornwalls are a flat 8 ohm load then try resistors on the speaker terminals to get it down to 4 ohms. The SIT-3 sounds best at around 4 ohm loads.

I don't remember which size resistors. Zu Audio would know and can make you a pair for your speakers.

I have Frankenstein Mk.II 300b mono's and a SIT-3 amp which I use with my Horning Eufrodite Ellipse speakers. I do like the 300b's better, but for SS amps they are really nice!

You can shoot Nelson Pass an email and ask him what would be best. 
He is very responsive and helpful. Maybe you are good without any because your speakers dip down below 8 ohms. You just don’t want them at higher than 8 ohms.