For what is worth I have been auditioning with a plan to buy using a loaned HiCap & a Dual TC
I've since bought a single TC as thats all I need on a Supernait.
To my ears & in my system the TC & HiCap sound is similar but there are clear differences in 2 areas. The most noticeable difference is bass which with both PSU’s is probably the most obvious change over a bare Supernait. The TC has no noticeable gain in the upper bass regions but does have nice progressive gain towards lower bass.
The HiCap bass is at first impressive with more of it throughout the whole bass range. But with my system (speakers) it was too much & became tiring on bass heavy material at higher volumes.
The second main difference is the TC has a more open realistic & airy presentation, it has more textural information & is closer to the stage front than the HiCap.
But in all other aspects the changes with TC are the much same as with HiCap. Both make good improvements to the bare Supernait, better stereo, realism, texture & detail & if the only choice was HiCap I would be happy.
Final point is (IMO) the TC does not change the Naim “sound” any more than does the HiCap; with a Supernait at least. If anything the famous Naim PRaT is more in all areas with TC, but the HiCap the bass prominence might just spoil something in my system.
My reasons for not choosing HiCap; bass prominence, less open presentation & transformer hum.