Same going to Disk Basic from MSX-DOS prompt.
Ah, when I use the openMSX IDE extension + memory mapper on an MSX1, MSX-DOS2 does boot indeed 
Not sure why though, perhaps the emulated mapper initializes itself? And apparently your mapper did too?
It's probably sorcery 
I think it's the DiskROM who looks for the RAM and if it finds a mapper, it initializes it.
A RAM mapper. When I put my 4MB RAM card on the 20P I also used my CF-IDE interface with DOS2. All very fine.
Wrong! CF-IDE interface uses a patched MSX-DOS2. This patch makes it work but not everything works very fine. For example, if you enter MODE 80, you will have the text displaying incorrectly.
It's convenient to use FAT16 patch by Okei specially with Multimente
It works but the CF-IDE interface supports bably the FAT16 with its original Rom-disk. It has a bug that makes not possible to fill more than half of the partitions. It only works well with the Nextor driver. These issues are noted in the wiki.
LPEMMC-SD also works with MSX-DOS2. But I think CF worked better. Patch can be a simple mapper initializing routine.
You don't need to enter Mode 80, it's not mandatory.
The SD cards I had to use on several machine were autoexec.bat-less to don't start MODE 80 and/or Multimente, unlike the ones I used to bigger things, who had it.
I have not much complains with CF-IDE. It can even play EVA files. Those are the MSX-DOS2 I have access, CF and LPEMMCSD. The good old ones, won't find any on my hands. Pretty much easier to flash any MSX-DOS2 version you want, patched or not, on a normal FlashROM cartridge. Or Nextor if you prefer. Never used it, my stuff is quite obsolete 
The patch just removes the condition on the adresse 002Dh from the Bios.
Ever simpler then Usually the best solutions are the simplest ones.
I use the Sunrise CF interface with Nextor 2.1.1 beta 2. It is much better with Sunrise's original ROM with the patched MSX-DOS2. Apart from the fact that the slave slot is no longer usable. CD-ROM drives are not usable too but I have never used it on MSX.
Meh, I used CD when I got the normal IDE, at first. (wich I still have, now you say it, I should sell it, cause never used it anymore, having the CF one) But well, quite pointless having an CF card and almost zero soft on CD 
I never tried the Knightmare Gold I think.
Haha, in the end, I lost the point about what the original poster wanted to achieve 
I had a CD-ROM player connected to my Gouda SCSI interface and I only used it to view photos from it (JPEG files.)