Its been awhile (like 20+years) since I have done anything like that. But if you post your autoexec.bat and config.sys files someone in here may be able to help?
Also for some reason in the back of my head I am thinking the cd driver was kinda of big in memory with some versions of it and you had to play memory jenga to get it just right. But that could just be my creaky old memory playing tricks on me.
Dont remember correctly, but you may be able to specify where in memory things land? It could be it is just not able to find a spot in memory for it. http://www.computerhope.com/lhhlp.htm
This is also popping up in my memory but you had to play around with where emm386 ends up or you could end up with it not working quite right? Like I said it has been awhile.