Thank you all for your advice. Unlike my previous Infiniti, using the XM cassette adapter which was actually louder then the cd player and twice as loud as FM...
1) Subaru FM sound is almost as hugh as FM or CD.
2) But using the aux input via JazzyMT was 1/2 even when all the way up.
Hence:
I already have a bid on ebay for the CMoy Pocket Amplifier