I have an ACT HDSS on my IX. Holds really well at stock+ power levels but is significantly stiffer than stock. So much stiffer than stock that eventual breaking of the clutch pedal mounting bracket (which is no longer avail from Mitsu) or the firewall itself is a real concern.
The ACT HDSS does not like to be continuously slipped for stop and go traffic on a hill. At a stop sign is not a problem, but stop and go on a long grade is a problem Sometimes I have to creep up an 8% grade for 1 mi hill in stop and go traffic and it's absolutely brutal on the clutch (and likely most clutches).
Spend the money and get a twin disc. Cheaper than fixing a torn firewall.

 

Take your Evo 9 to an exhaust shop and have them make a muffler test pipe. https://www.evolutionm.net/forums/ve...evo-8-9-a.html

 

can you even do this if the test pipe already has a cat? (STM Hi Flow test pipe)

 

I've had this HKS Silent Hi-Power https://stmtuned.com/products/31019-...ilent-hi-power on for almost a year and love it. Resonated, stainless, low db at idle, JDM bumper fitment. Night and day difference from the Greddy.

The mid-pipe on these cars is pretty straight so welding in a resonator is easily doable by an exhaust shop. As for clutches, owners have been loving ACT HDSS for years.

 

My exhaust was too loud for me so I lined my trunk with a sound deadening called Kilmat Extra that I found on Amazon and was pleased with the results. The matting doesn't get in the way of the trunk liner so it's all hidden as well.