You can simply state whether you like the song and what you like about it....vocals, instruments, sound of the mix..... most folks here are into the mix and compliments and advice (if you can give it) are always welcome. Simply take the time to go down the SONGS FORUM page, have a listen to each song there, post a comment and in short order, you will have the number of posts needed to post the links to your stuff, and now people will recognize the name and listen and return the comments on your stuff.
If you want advice on a specific thing...simply ask.... example: I think the bass sounds to weak and the guitars too flat..... people will advise. Or simply state: All comments welcome on the mix.
Once you start a thread or post in a thread, it's there and is not deletable by the poster. Measure your words carefully, however, you can delete and edit the contents of the post.... you just can't remove the post.
CLINTMARTIN: Yes, you can use 3rd party plugs in MC6. I ran MC4 for better than 3 years and used NI plugs, as well as Melodyne and many others without any problems.