Despite the many self-assured responses you received, no one can really analyze the phono gain inherent in your system without also knowing something about your amplifier and speakers. First, the SPLs coming from your system depend not only upon the output from your preamp but also on the input sensitivity of your amplifier. Input sensitivity is defined as the signal voltage required to drive your amp to its full output. Typically that is anywhere from 0.5V to 2.0V, somewhere in there. After that, we need to know the efficiency of your speakers and the size of your listening room.
But we can say that a cartridge that puts out 0.3mV into a phono stage with 58db of gain will result in a signal voltage of around 0.24V at the output of the phono section. Bear in mind that the figure of 0.3mV is published by the manufacturer for a stylus velocity of either 3.54 or 5.0 cm/sec. Most music will actually push the stylus around a bit faster than the standard velocity; thus usually the rated output is a bit pessimistic as far as the actual overall gain you get. Then that signal will go through the linestage of your preamplifier, which according to data posted by Chakster, adds 7db of gain, for a total signal voltage of about 0.5V. Depending upon the input sensitivity of your amplifier, that might be close to enough if not quite enough to make your listening experience a happy one. (To make these conversions of db to V, I use calculators available to anyone on-line. You should learn to use them too.)
I don't at all agree with the insistence of a few that a SUT is always superior to a high gain phono stage, but if you do choose a SUT, you MUST connect it to the MM input of your phono stage, which we know yields 43db of gain. The difference between your high and low gain inputs is therefore 15db. 15db of gain is equivalent to a voltage gain difference of 5.6X. You want a SUT that adds more voltage gain than that, because you already know (pending further info about your amp and speakers) that 58db is not enough. Your cartridge, which has an internal resistance of 5 ohms, according to someone, will work fine with a SUT that has a 1:20 turns ratio (a voltage gain of 20X). That combo of 43db gain from your MM stage plus a SUT with a 1:20 turns ratio should put you in a safe area for total gain. 1:10 might work too (voltage gain 10X).
I think why many others think 58db should be "enough" is because most linestage sections add more than 7db of gain on top of the output of the phono section, more typically 10 to 20db. That may be why the consensus is you should have enough gain already. Plus we don't know about your amplifier.
