Recently I've begun to occasionally operate my FT-1000MP on 10M and 75M AM, 
something I used to enjoy way back when I was a newly licensed general (WB2RNL) 
with a then modest setup of a 75A1 and Valiant.  Since SSB was the rage, the 
AM/CW equipment was quite inexpensive during that time.

I've been pleasantly surprised to find that the FT-1000MP is quite an excellent
AM rig, in terms of both transmitted and receive audio.  It seems that Yaesu
has generally done a far better job than Icom or Kenwood in providing AM capability.  

Receive
I've been using the stock 6.0Khz filter, although I suspect the wide INRAD filter
would offer some improvement in skirt selectivity.  If the received signal is not
too weak, I use the synchronous AM detector.  Normally I find that synch AM provides 
a higher fidelity receive signal.  I've also been using the dual receiver in stereo - 
synch AM on the main receiver/left ear, and standard AM on the subreceiver/right ear.  
First zero beat the signal in the main receiver and switch back to AM and press A -> B
and DUAL.  This gives a nice stereo hifi effect.


Transmit
I've been using a Marshall MSL 2003 condensor mike with a small amount of external 
processing through a Behringer VX-2000/PEQ-2200 combo. Please refer to my MP Setup page 
for the proper MP settings that would be suitable for your audio setup.  I've been 
getting consistently excellent reports on my AM audio quality.  From what I've heard 
on the air, Yaesu transceivers (and microphones) of all vintages sound quite good on AM.

Mic gain should be adjusted to show minimal deflection on the ALC scale.  Adjust the gain
to sound perfectly clean with no clipping on the internal monitor.  It's also helpful to 
initially adjust the audio while monitoring the signal on a second receiver.  Adjust the 
carrier output for a maximum of 25 watts.  I routinely use an Alpha 99 amplifier, which I 
can drive to 300+ watts carrier output with far less than 25 watts of drive from the MP.