Capacitor

@jasbirnandra 

I have custom built 2A3 SET amps and I don’t know what the input impedance is. I doubt it’s even close to as high as your Canary 300B, but I think it’s high enough to use a cap much smaller then 3uF.

My big concern was the interstage capacitor. Grannyring’s post confirmed my concerns. For the interstage capacitor, I (and you) need to stick to 3uF. 

I have written to Canary to confirm what the 3uf capacitors are for output or interstage lets wait for their mail

@jasbirnandra

I cannot speak for your pre, but I’ll share what I have on mine.

I have 4 x 3uF coupling caps.

1 pair (the pair towards the back of the chassis) are output caps. I confirmed by measuring the resistance between the output RCA and the cap’s red lead and measuring between the 2nd pair of 6SN7 (the pair towards the back of the chassis) plates and the cap white lead. 100% they are output caps. This pair I may consider going smaller to get the best quality cap.

The other pair are interstage caps. I confirmed by measuring the resistances of that caps red lead with the grid on the second pair of 6SN7s and the cap’s white lead with the plate on the first pair of 6SN7s (the pair towards the front of the chassis). 100%, they are interstage caps. This pair I will stick to 3uF.

My pre also also has 2 pairs of 0.01uF caps - one per 6SN7 tube. In both cases the red lead is connected to the grid of triode 1 and the white lead to the plate of triode 2. IOW the two triodes in each 6SN7 has a coupling cap. I’m going to do these first as this is much cheaper - I just have ordered some VCaps a few minutes ago.

Note, this is the C800 MK2. How your pre differs I don’t know. I’m simply sharing what I have found.

Why do you think changing caps will give you the desired results?  It's the entire preamp design, not one circuit component, that makes the difference.

You'd be better off selling the unit and searching for a different one that will give you the performance you want.  If you change one cap in the circuit, the manufacturer may decline to make repairs to such a modified unit.