Dear @ryzhu,
Each individual file can be compressed (zipped fastq/fasta), but a zipped collection of files will not work. 8 GB of 6 files would approx mean 1.3 GB per sample, which can be technically done by the Galaxy upload. Yet, this might take some time. If it fails, or it takes too long that an FTP upload might be better.
Kind regards,
Florian