Disk won't mount Microsoft Basic Data
The asr target option --settype "Apple_HFS" modifies the GPT partition type but not the file system. So the partition "content" is 48465300-0000-11AA-AA11-00306543ECAC (which is an indicator for a normal HFS+ partition) but the file system on disk6s2 still is NTFS/ExFAT/FAT32.

If the disk is empty, simply erase it with Disk Utility to whatever you need. 



Changing the partition "content" with gpt or another similar tool doesn't alter the file system. Your volume may not mount if content and file system don't match! 

BTW asr is not the proper tool to format volumes, create file systems or to change the partition type. This is rather done with newfs_XY, diskutil and gpt.

To determine or examine the file system you would have to open the volume as raw data and check for specific headers or fs structures.