Just put the sound files in a folder named sound.RR, then edit the aircraft.cfg and change the line sound= to sound=RR.

I'll use the ANA 777-300 as an example.

Here is what it looks like by default:

[fltsim.0]
title=CS 777-300 PW Captain Paint0
sim=csx773_PW
model=300_PW
panel=
sound=
texture=ana
kb_checklists=
kb_reference=
atc_id=JA753A
atc_airline=ANA
atc_flight_number=777
atc_heavy=1
ui_manufacturer=Boeing
ui_type="777-300 PW"
ui_variation=All Nippon Airways
ui_typerole="Commercial Airliner"
ui_createdby="Captain Sim"
engine_type=PW 4098
description="777-300ER PW JA753A (cn 28273/132)\n777 Captain 1.2\n(c) 2013 Captain Sim www.captainsim.com"

And here is what it has been changed to so that it uses the sounds found the in sound.RR folder:

[fltsim.0]
title=CS 777-300 PW Captain Paint0
sim=csx773_PW
model=300_PW
panel=
sound=RR
texture=ana
kb_checklists=
kb_reference=
atc_id=JA753A
atc_airline=ANA
atc_flight_number=777
atc_heavy=1
ui_manufacturer=Boeing
ui_type="777-300 PW"
ui_variation=All Nippon Airways
ui_typerole="Commercial Airliner"
ui_createdby="Captain Sim"
engine_type=PW 4098
description="777-300ER PW JA753A (cn 28273/132)\n777 Captain 1.2\n(c) 2013 Captain Sim www.captainsim.com"

This will affect any variant that you change the sound= entry on.

Hope this helps.