Cartridge incompatibility, Soundsmith and Luxman

Finding that load resister is not hard. It will be right off the phono input @retipper has already joined this conversation and is obviously loath to give himself business by making this suggestion but, I would suggest acting as an obvious shill for Soundsmith that you send him your amp and he will be happy to make that modification and sell you some loading plugs for a very reasonable cost.

How does the Luxman sound when playing other sources, such as CD player or streamer, as compared to your prior rig?  It would help to know if the basic sound of the Luxman is to your liking.  If you like the sound, then it is the phono stage that is an issue (either not very good, or incompatible with your particular cartridge or other aspects of your set up).  How much have you experimented with other aspects of your phono setup--have you played around with VTA, for example?  A higher VTA (pivot of tonearm elevated more) will tend to shift the tonal balance more toward the high end.

Larry, If you read the responses, you will know that the problem is almost certainly the fact that the fixed value of the load resistance at the phono inputs of the Luxman is 100 ohms.  The Zephyr is a rare low output MI type, which has high inductance compared to a typical LOMC type.  Thus it needs a higher value load resistor.  The high inductance cartridge into a 100 ohm load would be expected to exhibit all the characteristics that the OP is not happy with, and justifiably so. That issue would have to be dealt with before one could fairly evaluate other elements in this system.

First, I'm not going to open up the amp and modify it. By the time I do that, I might just as well spend the money to get a different cartridge. Yes, I do like the Zephyr, but there are other good ones out there.

Larry, yes, I do love the sound of the 590axii. It's ONLY the phono that sounds extremely dark. Switching to a different cartridge (I have a spare MM cartridge) opens up the highs to be just like my streamer (or CD for that matter). It's a compatibility issue between the fixed load and the cartridge.

I have read the responses, and in fact, I suggested a cartridge with a source impedance below 10 ohms, in acknowledgment that that might be a way to avoid the incompatibility problem.  I just wanted to be sure that the OP did not get off on the wrong track.

I hesitate to offer specific recommendations because cartridge preference and system matching is so personal.  If I were to hazard a guess, a Lyra cartridge might be a good match--most have quite extended highs, a very clear sound, and have a fairly low source impedance that would be compatible with the 100 ohm loading of the phono stage.  I own an old Lyra Titan and I like its sound, although these days I run a Transfiguration Orpheus L.