I have tried some of those in my Dialogue Premium integrated .
The Cifte's were rather boring and uneventful . A friend of mine tried them in his Ayon and didn't find them pleasing either .
The Amprex were an improvement in all directions . Nice bass , air , bounce and musicality . My second favorite input tube .
For less money , the RCA Cleartops come close to the Amperex's and actually do better with voices .
The CBS will favor female singers with slow jazz . Very accurate but not as musical as the Amperex and RCA .
My favorite is another Dutch tube , the 7316 . A step above the Amperex with the inclusion of the RCA voice aspect . Just an all around winner , for me ! The earlier production the better and probably the most expensive .
My integrated has 6 input tubes as does your preamp . I found that changing just the front two tubes , on each side , was enough for the desired change . I leave the rear 12AU7 on each side stock , the Primaluna . I did not note a discernible improvement by changing these rear tubes .
Now , a word of caution with these tubes that I like . I have very neutral speakers , Reference 3a Di Capo i's . So I prefer a warmer tone that what you may desire with your Harbeth's which tend to be a bit warmer .
Maybe try the RCA's , which are cheaper than the Amperex and 7316 to see how they work in your situation , they are still a nice tube .
Good Luck
