How much midrange bloom is needed? With other words: can you have too much midrange bloom? When does midrange bloom becomes an euphonic coloration?
It is worth pointing out that Frontier1 is baselining against the excellent ASL Flora, which is not displaying the excessive bloom. This suggests that the issue may be specific to the VK52Se. Frontier1 already reported this bloom to me before replacing the SovTec 6H30PIds with the DR NOS Supertube variant.
How many hours do have on this unit? Most take 200 before sounding their best. Some interconnects can interact and cause anomalies as well. If this is a new unit- give it some time. You can burn it in by playing your CD (on repeat) through it with your power amp turned off. What did it sound like with the original tubes?