[cmiovino]

I've played with intakes on various NA Subaru boxer engines over the years. I do get the sound you're chasing - basically an exposed cone filter. Which in short ram or "hot" intake variations are bad for power and can even lead to detonation in extreme heat instances. Cold air intakes I've seen suck up water and hydrolock engines in a few cases, plus the filter sometimes is too far away for the sound you want.

In either case, the cone filters generally need full intakes to work, which ALL should be tuned for because ALL vary the MAF scaling. Now, whether or not the ECU can adjust for any variances is how manufactures get away with saying "no tune needed" sometimes. The problem is all deviate away from the MAF scaling tables, some more than others.

As others have said, stock intake with a drop-in filter is the way to go. Retains the "cold air" aspect of the OEM intake, is cheap, and basically makes the most power. It's just not a restriction. If you want a fancy pipe, the Perrin intake tube is another cheap addition that doesn't require a tune as it's not changing the pre-MAF sensor flow or the housing the MAF sits in.

IMO, any sound changes you want should be done via the exhaust. Much safer this way.