I really wonder when I hear the voice of their vocalist.

He sounds like a real siren: magical, erotic and warm, but he also has a really cool extreme vocal.

I wouldn't consider a siren magical, erotic, and warm. A siren is a device that makes loud annoying sounds.

I don't like an extreme vocal sos as much like as clear vocals, but Hoah (vocalist) is an expecception.

I was really in wonder when I heard the voice of their vocalistsinger.

I assume this is what you meant. In English, when someone says "I really wonder..." that means that they are curious or have a question. If you are in awe of something then you are "in wonder". For example, you could say "I was in wonder when I heard the voice." I assume you also used the past tense for this and that you are talking about something that you had seen, rather than something that you are currently seeing.

Also in English it's less common to call someone a vocalist unless they aren't singing any lyrics and are providing a vocal background of sorts in a piece of music. Assuming that this isn't Hoah's role, then he would be a singer and not a vocalist.

He sounds like a real siren: magical, erotic and warm, but he also has a really cool and extreme vocalice.

For this, both "sounded" and "sounds" could work. But if the vocalist sounds worse in the future, then you could only use "sounded" since his voice would sound bad in the present. Also, I assume you know what 'erotic' means. Don't use it often, it's a bad word.

I don't like an extreme vocal soice as much likeas a clear vocalice, but Hoah (vocalist) is a expecception.