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!

I have an analagous setup with Nelson’s First Watt clone Aleph J and Crites B speakers which I have enjoyed for several years now. Better than stuff costing 1000s more, collecting dust now :-(

I still have a set of the Zu resistors... thought they should be a different value

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.