SUT suggestions for Audio Note System

Here are the specs for the M6 phono.
The overall specifications for the M6 RIAA phono preamplifier are an input sensitivity of 47 kΩ, an input sensitivity of 126 mV for 1 V output, an output impedance of <10 Ohms,

Thanks Bob but the research I have done shows it being .6. There are 2 blacks. Mine is the early one if that makes a difference. 

Some people have asked for the specs of the M6 phono here they are below.

—INPUT IMPEDANCE

47KOhms Phono

-INPUT SENSITIVITY 126mV for 1V Output, Line Level

-GAIN @ 1KHz

68 db phono

16dB Line Level

OUTPUT IMPEDANCE <10 Ohms

OUTPUT NOISE (RMS) <0.08mV unweighted, Line Level

<15mV unweighted Phono

internal impedance of the Koetsu black is 5 ohms

Thanks very much for taking the time to look into the specs. 3 posts above I mentioned the specs of the m6 phono V4. Mine is a V2 so there could be a difference. Did the specs that you found come from a version 2 manual?  The V4 manual shows the phono at 68db and the line at 16db.  I thought I would mention this as it does change the end db figures.  I’m not sure if those numbers make a difference or not. Again thanks for the effort. 
 

I am starting to Leen the way of getting a quality multi setting SUT to allow for trying other cartridges. Any thoughts on that?

Update

So I hooked up a MM high output Grace F9 up to the M6 phono. It was far too loud. Even 1 on the dial was too loud for late night listening and four was a very uncomfortable level. Dover suggested that I hook my Koetsu black MC straight into the MM phono. So I did that and the volume is perfect. One or two on the dial for late night listing 3-4 nice comfortable daytime listing and 5 if I want to push it. So the question is did I just saved myself $5K on a SUT or am I missing something by not using an SUT. It is evident that I could undoubtedly use a low level SUT which means I could find a used Audio Note as they are usually available..

I spoke with Audio Note and they told me that it would be fine to run the system this way but I am leaving sound quality on the table by not matching the impedance of the Koetsu. The reason I am able to run it this way is because of the amount of gain I have in the system. The amps are 18 W, the M6 has a lot of gain, and my speakers are 98DB. The solution is to modify the amplifiers to the low gain version which is not difficult or costly. I then have to get a medium output SUT in the 15 to 20 ohm range. And here I thought I could save some money. LOL.