Pierre,

Regarding the mic, I have to acknowledge that Uncle Dave has more personal experience of mics than I have, and so I respect his opinions. My experience is mainly from the mixing side.

It is certainly true that SM58's are old - I have been using them for probably in excess of 10 years. However, SM58's are still being manufactured and sold because they are recognised as being good mics. I have never had any trouble with them, and do not have to apply any EQ due to the characteristics of the mic.

In my opinion, the best test is your ears. With an amplifier running at a nominal level (neither too loud nor too soft) a singer should sound as close as possible to their natural sound, assuming you are not adding reverb, etc, and that all EQ settings are at their midpoint or completely bypassed. This needs to be true over the full frequency range and dynamic range of the singer.

There are other characteristics too look for, but these are fairly common to all good quality vocal mics. For example, a cardiod mic minimizes extraneous noises, such as sound from a nearby drum kit (including the drum kit in your KN6000). I notice the mic you mention (e845s) claims to be super-cardiod. That maybe good provided it does not give you too small an angle of pickup. If it is too small then your amplified volume may fluctuate if you move around too much in relation to the mic.

Good luck