Most of my metal music collection is in FLAC.

Should I upload music already in mp3 on the tracker? This is real FLAC not re-encoded mp3. For example I have slayer studio discography in FLAC. mp3 discography already uploaded.

Most of my FLAC collection comes from demonoid and rockhard lossless.

Yes, you can upload.
Torrents with MP3 and FLAC are differ. Both can be uploaded to our tracker.