There's a few things here I don't really understand.
You've said you're using a 4.3Gb HD, yet partitioned it into two volumes: A/ 2Gb, B/4Mb? Why only 4Mb? Why didn't you create two partitions of 2Gb each and run 7.5.3 on one partition and A/UX on the other? I don't understand why on a 4.3gb disk you're only actually using 2Gb 4Mb of it.
The first thing I think I'd try is reformatting the drive with the standard Apple HD Setup that comes with 7.5.3 into one HFS partition and installing 7.5.3 onto that and see if it boots the machine. If it boots it successfully, then it either doesn't like the Silverlining SCSI driver or 7.5.3 doesn't like sharing the partition with AUX/7.1
You've said you're using a 4.3Gb HD, yet partitioned it into two volumes: A/ 2Gb, B/4Mb? Why only 4Mb? Why didn't you create two partitions of 2Gb each and run 7.5.3 on one partition and A/UX on the other? I don't understand why on a 4.3gb disk you're only actually using 2Gb 4Mb of it.
The first thing I think I'd try is reformatting the drive with the standard Apple HD Setup that comes with 7.5.3 into one HFS partition and installing 7.5.3 onto that and see if it boots the machine. If it boots it successfully, then it either doesn't like the Silverlining SCSI driver or 7.5.3 doesn't like sharing the partition with AUX/7.1