Incbin?

I'd say that

org $9000
Incbin "blah.rom"

won't really work. It's just an indication for the assembler to generate code assuming that it starts at that address, but the ORG won't do much when including the file.

The second way makes more sense to me.
Other option is to add some padding in the first case to ensure that your binary actually starts at that position. For example, to add segments in a megarom.

It does not really matter if you use DB or INCBIN... It is just data. If you ie. have a HELLO.TXT file that contains "HELLO WORLD!" as text you can either do INCBIN "HELLO.TXT" or you can include the data to source file by writing DB "HELLO WORLD!" Once the source is compiled the data is part of your output file and changing source or the HELLO.TXT does not affect the compiled file unless you compile again.

How you get the data to correct address is then another thing, but I would not use ORG. Try ie.

DEST	EQU $9000

	LD HL,DATA
	LD DE,DEST
	LD BC,DATA_END-DATA
	LDIR
	RET

DATA:
	DB "HELLO WORLD!"
DATA_END:

DEST is just a constant in the previous exemple.
The adventage of NYYRIKKI method is that you don't need to dicide the data address in advance. The label will tell the linker where your data are located into the final binary.

If your data is formated to work at a given address, this method don't works.