If it's working on his DSi XL, then he should update the Acekard's firmware while he has the option. Many consoles have their firmware updated accidently, or unknowlingly updated by another person.
To answer the question, use the 1.4.1 'Alex Stormrider' update. If your DSi has firmware 1.4 and your Acekard has the 1.4 'Danny Phantom' fix applied, then you should be able to use the console to perform the 'Alex Stormrider' update. An Acekard with the 1.4.1 'Alex Stormrider' fix will work with a console that has FW 1.4 as well as those with 1.4.1.
Guide to updating the firmware
http://gbatemp.net/index.php?showtopic=231410