RHF wrote a pretty good assessment overall:

Icom IC-R75 (R-75) Performance Upgrades by Kiwa Electronics :
KIWA = http://www.kiwa.com/R75.html

#1 Must Do = Kiwa Synchronous Detector Upgrade

YES! The AGC fix here is key.

# 2 Should do = Kiwa Audio Upgrade

YES! A big help, nicer audio.

# 3 Worth doing with #2 = Kiwa High-Fidelity Audio Filter

Yes, but note that this may *slightly* increase the potential to induce
audio heterodynes. I think that potential is small, but check with
Craig at Kiwa.

# 4 Do only 'if' you are into AM/MW DXing then get
the "Full" Mod Kiwa AM BCB RF Attenuator Disable

Maybe. This provides only a 3dB increase in the MW sensitivity, and if
you have AM blowtorches near your house, it may adversely affect SW. I
find that my own radio is plenty sensitive enough on MW, and the nearby
stations are patently obnoxious.

# 5 Worth doing 'if' you don't like play with the Twin PBT
and simply want to select a Filter = Kiwa R75 Filter Module

The old filter fix was a better one (see below)...

My Icom IC-R75 is a few years old and has the original Kiwa Mods :
* Kiwa Synchronous Detector Upgrade
* Kiwa Audio Upgrade
* 3.8 kHz IF Filter Upgrade for 450 kHz AM-Sync
(not available any more)

Same as mine, plus I have the 15 kHz filter reduced to 6 (which is
plenty wide enough for AM but affects FM modestly). That old filter
fix was the cat's pajamas, yielding an excellent array of filtration
plus ability to filter on AM and S-AM both, and very flexible use of
the PBT. The new one, apparently, does not give the full flexibility
on S-AM or with the PBT (no fault of Kiwa, BTW - he's doing his best).

Fie on Icom for creating a potentially excellent radio with a bunch of
goofy flaws!

Bruce Jensen