O.,

the impedance mismatch is a problem - but yours sounds more dramatic
than it should be. Someone posted instructions on how to build an
impedance matcher yourself here a while ago, which I will repost below:

No need for field mods, nor for active components. If you have any
soldering skills, pick up a couple of 8/1000 ohm matching transformers
and a male/male mini-plug cable from Radio Shack. It's a minor
impedance mismatch problem. I put one together for my Cirrus and it
boosts volume by more than enough, and it's completely passive so
there's no batteries or other stuff. One of my fellow Cirrus brethren
came up with a great packaging hack--a small prescription pill bottle
is big enough to hold everything. Drill a hole in the bottom and in
the lid, tie knots for strain relief, and it's all quite tidy, if a
mite funny looking.

Dave;
Do you put one on each side (of the output)? And is that what I ask
for? An 8/1000 Ohm matching transformer? Thanks again

om: Dave Katz
Newsgroups: rec.aviation.owning
Subject: Music in Intercom
Date: 25 Jul 2002 10:00:59 -0700

Yep, one for each side if you want stereo. The low impedance side
(red/white) goes to the audio device, and the high impedance side
(green/blue) goes to the Garmin. You can snip off the black center
tap on the high side. I hooked the white and green leads to the
common (sleeve) connections on each side, but I don't suppose that
it matters so long as you're consistent (so you don't phase-reverse
one side.)

They were the only transformers for sale at the Radio Shack at which I
got mine. They may just be called "audio transformers" or somesuch,
but
it'll say 8 ohm/1000 ohm on the packaging.

--Dave

Thanks! I saw them at RatShack, about 3 bucks each. Total of about
12 bucks with all the other special goodies like a 2 dollar project
box and 4 dollar cord.

--
Thomas Borchert (EDDH)