hello Amir,
You said you bough 3rd party styles, with no voices included I guess(?), which means styles are using preset (built-in) voices. I say that, because in this case we can't really blame voices characteristics.
Now you mention that loudness (=volume) isn't really the problem: it's the "punch" that's too loud. In this case we are probably talking about some drum (within DrumKit voice), but can also be a bass guitar -anyway, a voice that has steep/fast attack. That is, if we decrease drum volume, there will be less punch, but actual drum sound (decay) will will also be quieter.
In this case two solutions come to my mind:
1. In style, try to replace drumKit (in Rhy1 or Rhy2 channel) with another one and re-adjust drum volume if necessary. As we know, most DrumKit's (Standard-, Studio-, Analog-, etc.) sound very similar -but the difference is in detail!
2. Open style in Style Creator and by using Step Edit, find the problematic percussion (within DrumKit) and decrease it's velocity to your liking.
The above also works for adjusting any other regular voice within style. The difference is, in this case we can also modify attack time (
Reference Manual p. 48).
Btw. if MegaVoice is used for bass guitar, then try with a normal bass voice.
Bogdan