What kind of floppy disk do you have mounted? The BIOS only supports up to 720K and up to 360K low-density disks(everything from 1.44MB and up isn't supported).
MS-DOS 3.3 originally booted ok (360K floppy), newer might not work.
You might also go the easy way: create an empty hard disk image, use an bootable 360K MS-DOS 3.3 floppy and dummy(XT-IDE) ROM, Flash it from the floppy over the XT or AT ROM using UniPcemu(or simply use Dosbox to create a XT-IDE ROM with manual configuration) to use the ATA IDE HDD interface at the default IDE ports, save it back to the file, use the file as HDD ROM. Only the primary controller is used(Secondary contains CD-ROM ATAPI devices, which XT-IDE can't handle). The base ports are 1F0 and control port 3F6.
The full details of the HDD controller ports is at: http://wiki.osdev.org/PCI_IDE_Controller#Dete … _IDE_Controller
The PCI autdetect way is also supported, but for some reason xtidecfg only sees the Secondary(CD-ROM) controller in UniPCemu. Once configured and flashed to the ROM(See the UniPCemu wiki), it should find the harddisk correctly both on XT and AT.
The AT floppy disk is mostly accurate, only disk read/write timings are still unimplemented. That makes it give the 601 floppy errors.
Last time I checked, Turbo XT BIOS ran fine booting from 360K MS-DOS 3.3 and reading(not writing!) 1.44MB+ HD floppies.