Hi Dean,
Question still remains, why you want SDX as newbie?
Yeah, good question. For me easy to follow.....
Normally ATR must be mounted using a SIO.
If you have no SIO-PC link, you need to use your MyIDE-II with MyBIOS for ATR-access.
OK.
Add this in your CONFIG.SYS
USE BANKED
DEVICE SPARTA
DEVICE SIO /A
.....
Create a partition D1: 2000 sectors DD. (load MyBIOS-F2, hold START+SELECT+OPTION, Make.....)
PC: With the DriveManager LBA2 copy the toolkit to partition D1.
Back to the ATARI:
Load MyBIOS-F2, press SHIFT, select fat32-loader, load SDX.
Now you have loaded SDX with MyBIOS-F2 as alternative OS for MyIDE-access.
D1: should now be the toolkit.
run FDISK
Create partitions.
Copy D1 (MyBIOS) to a APT-partition.
Now you have the toolkit in APT and you can omit loading MyBIOS-F2 the next time.
That is if you want to use SDX only.
Not easy, but SDX is for heavy users

FAT32-loader:
all you need is on this link:
viewtopic.php?f=17&t=1330