@fjn04
my further input to you is as follows as you decide in your own case
1. with c7’s on proper stands, a key variable as you probably know is how they are placed in the room w.r.t. room boundaries and boundary bass reinforcement - this aspect in my experience with all harbeths (other than the teeny p3’s) is really important to dial in to get the best possible presentation and relative balance of bass and mid bass in relation to treble and midrange
2. c7’s are also a pretty benign 6 ohm load, so most decent tube amps will drive them to reasonable volumes... the issue is the quality of sound that is produced, and specifically the overall sense of transparency and sufficiency of bass grip/impact
3. i have always felt that all but the best tube amps (in my book, the higher audio research ones) left the harbeths bass slow soft and sloppy, so thus i have ended up always using top solid state amps that have vastly superior bass control (and sweet sound up the range)... also the better ss amps bring the c7 treble response forward some, which is to my liking - once again, my ears my room my taste
4. more traditional sounding tube amps to me entirely mirror and accentuate the c7’s nature - midrange lushness, treble reticence, full midbass and somewhat weak/slow deep bass, so to me, they bring negative synergy - but i could see such tube amps working if one uses powered subs to augment (i tried this, i have a pair of rels, but i still felt the midbass, while rich and full, lacked my desired level of definition and speed)...
hope that helps, good luck