Consensus of net opinion seems to be that the only real options are K&N (my choice)
http://www.knfilters.com/ or ITG - oil impregnated, last forever and better air flow. Also easiest and most stock looking is purely replace the OEM panel filter with similar from the above.
Some say you can get more air through replacing the complete box approach with a high flow intake (again K&N or BSR)/ Induction type but you need to ensure shielding the air inflow from the heat of the engine. But some say you never get the real benefit unless you get true cold external air so they pipe the air intake accordingly. Friend of mine had that as standard on their Renault (Espace) and it would act as a water input channel straight into the turbo with needless to say, detrimental results.
Hope thats of help!