Cartridge incompatibility, Soundsmith and Luxman

If you cannot find a technician to switch out the built in loading resistor (assuming this IS the issue), and you are against using an external SUT feeding the MM input, you will be in the still troublesome spot of finding a cartridge that works.  Do you have a dealer that is willing to allow you to audition cartridges or allow you to bring in your integrated amplifier to see if sounds okay with particular cartridges the dealer has to offer? 

I would hate to hazard a guess as to which cartridges might be compatible, not only with your integrated, but with the rest of your system and your particular taste.  The 100 ohm fixed load suggests a cartridge with a low impedance of the coils in the cartridge itself-at most an impedance of 10 ohms, and much lower would be better still. 

Most low/medium output cartridges with a typical 0.4mv - 0.6mV output and ~ 5 - 10 ohms coils should work well with that Luxman MC phono. The carts like the SS Zephyr and (I'm guessing) Benz LPS / Ruby / SLR are the outliers that have any trouble. There are a number of MC phono stages that only offer a 100 ohm load, since it's a very typical value in this range. 

@lewm is right, he never advocated a SUT here. I don't think anyone was suggesting that, except OP. I touched on cable requirements for a SUT, but to be clear I definitely wouldn't try to throw a SUT on this thing (the JFET headamp is another deal entirely). 

It was me who pondered that there might be a SUT inside not Lew. I realize that many MC inputs offer a 100Ω option but I found 100Ω as the only option to be a bit odd particularly for something likely to be paired with a 40Ω denon 103.  Add to this that there are many who insist that a MC cartridge should be loaded at 47kΩ and the single 100Ω option seems like a very limiting choice for any active circuit but a perfectly logical one for an internal SUT.

dave

Cardas Clear Beyond sounds amazing, but they're not inexpensive...

Cut the cables in half, add 2x extra terminals and put the SUT in between?

There seems to be one easy thing to do and many crazy solutions. Umm.....please don't take the top off and modify or tweak your amp. There are a zillion excellent cartridges. Buy the one that fits the phono stage and have a great time.