I'm new to Step Up Transformers

Only 30 years?

Keep in mind that what you’re proposing, assembling essentially a collection of SUTs so one can experiment with mating to one or several LOMC cartridges in pursuit of a best match, can easily become very expensive, time consuming, and possibly so troublesome as to discourage one from pursuing the hobby at all. Perhaps it works for you, but it’s not tenable for everyone who otherwise wants to use vinyl as a source.

As a person who 50 years ago did build a speaker without knowing anything about crossover design (not speaker design because I blindly followed information contained in a magazine article), I’d say Atmasphere has a point. But if you read the pdf available at Jensen, you see they recommend a rather complex network of R and C to get correct loading. Almost no one actually does that in implementing any of the dozens of different SUTs mentioned on this and the many other threads devoted to SUTs. So what do all those reports mean or how should they be interpreted? With more than a grain of salt, I think.

I am constantly surprised when others report they hear important differences between two different load resistances, using LOMC or LOMI cartridges, that are numerically very close to each other on a scale of 100 to 47K ohms. Like 725 vs 525 ohms or 800 vs 1000 ohms. I believe the reports because they’re subjective, but I’m surprised anyway; I don’t hear important differences between such values. In fact I think of loading in terms of logarithmic differences. So i might try 100, 1000, maybe 10,000 ohms and then 47K ohms. If the cartridge permits that array of load Rs, I choose one among them but usually the difference in sonics is not dramatic. Atmasphere points out that one is actually loading the phono stage. Maybe my array of phono stages is less sensitive than some others. One thing I would not do is choose a load resistance lower than recommended. Notice that no maker sets an upper limit on load R. None say not to use 47K ohms.

I’d say wait through 2-3 listening sessions at least one hour each in length, before making any judgement of a new cartridge, and that’s only if you’re very familiar on a long term basis with the phono stage. And even then, cartridges do change over time from new, probably more so than any other piece of gear.

An MI cartridge with a 10 ohm internal resistance like the Paua and some other soundsmith MIs is not comparable to an LOMC with the same internal R, because LOMI cartridges have a MUCH higher inductance, at least 100X to 1000X higher than the LOMC. The inductance adds to the resistance as frequently goes up. Thus the recommendation for a 470 ohm load as a minimum. Dave Slagle mentioned yet another reason for the recommendation. I run MI cartridges with a 1k ohm load, minimum, usually 47K ohms.

Atmasphere is also all tube high gain phono, as I mentioned earlier. I’ve owned an MP1 for two decades upgrading along the way. I also owned an Aesthetic Rhea Signature but not the Io. The Rhea is amazing for its remote controlability but was a tad noisy compared to the MP1 when I cranked up the gain. 

The Herron phono stage, now out of production but possibly available pre-owned, is another that achieves high gain with an FET based input stage followed by an all tube circuit. It was very highly regarded, one might say venerated, by some who frequent this site, before Herron closed down.

There are many fine quality tube based phono stages that offer sufficient gain for a LOMC cartridge and do not contain a step up transformer internally. Many of those use a solid state or hybrid gain stage in order to achieve that goal (Manley, probably ARC), but some even do it all with tubes (Atmasphere) and that can be done while preserving a good signal to noise ratio, contrary to what some will say.