Related to post in os2museum.com (I love OS2), I used DR-DOS 3.41 more times than MS-DOS 3.3. QBX 7.1 runs fine using DR-DOS.
Unfortunately, updated DosBox-X.tcz remains with same error: Int10, Function EF00 not supported. Sound appears to be little better in this compilaton, but I still can not save .Bas files using QBX 7.1. :-(