Should I use an external Phono Preamp

The sonic one is looking for is only found by experiencing different Amplification of the sent signal. It is through experiencing different influences on an end sound produced that assists the user of the Analogue Source to discover the sonic traits that is most attractive to them. 

The more familiar that an individual becomes with the differences between end sound produced by different circuits and topology, will enable them to make educated choices to help them attain an Analogue Amplification that lends itself to ones unique preference for a produced end sound.

Firstly, My experiencing Aucurum Coil Wire is leading me to state that this wire type is capable of adding Richness of Tone, which is detectable in an end sound.

For myself when Aucurum Wire is used in the Analogue Signal Path, I prefer downstream support for the signal path to be auxiliaries to have a sonic trait that leans towards being transparent. 

If I am using a MM Input, the Step Up would be preferred using a Head Amp rather than using a SUT.

If the individual using a Cartridge with Aucurum Wire and is looking for a further injection of Richness of Tone. When the MM Input is being used, I would recommend the usage of a SUT. 

Either of the above are typically much cheaper than purchasing a Standalone Phonostage, and SUT's have for myself been both purchased and loaned items.

After my having used a reasonable range of SUT's, I am confident in my stating that differing models are capable of presenting different levels of noticeable tonal richness. The are SUT's I have not been in any way attracted to, more repelled from, due to the discernible tonal richness being detected in the end sound.

I have only had a small selection of Head Amp's used and these are always referred to as having discernible transparency.

For the OP, I have been to many demo's of Phonostages where comparisons between Phon's has been the reason for the demos being arranged. To date, I have not been a fanboy of Phon's demoed which are using Resistance Loading to interface the Gain required by a Cartridge.

For the OP, if Tonal Richness is wanted to be investigated, then an SUT and Head Amp may be all that is needed. Recently I added a link to a Post of a US Company offering home trial on their SUT.

If there is a want to improve the overall presentation, with improvement to micro dynamics, dynamics, detail, envelope. The search to discover the Phonostage capable of delivering this becomes much broader, I strongly recommend hearing any shortlisted in advance of committing, as synergy with the rest of the downstream auxiliaries is also critical to create a experience wanted to be maintained for a long time. 

I didn't mention I am using a Nordost Valhalla 2 tonearm cable. Maybe that could be improved?

What do you like or not like about your present system? What is your goal in adding an external phono? Surely your cartridge could be upgraded. Nordost cables always sound lean and bleached to my ears in my system.

My preamp came with a very good phono stage but adding a Gold Note PS10 and PSU10 made a difference. Beyond that, the ability to change load and gain on the fly is a definite advantage. 

For the OP, I have never been able to describe what I am looking for in an end sound heard with great conviction, until it is heard.

I have heard many end sounds resulting from a Phonostage Influence that I have not wedded to, but in the same system, also heard Phonostages I have felt are worthy of learning more about and how they can sound in another system, especially the home system.

Today, my main interest is in SUTs and Head Amps and how sound is produced using these as an upstream of the Phon' add-on. I have a few to try out on a list. 

Used with my newest Speakers, my very recently acquired custom design/built SS Phon' is exceptional in its early usage condition using the MC Input. Using owned SUT's into the MM Input, has caused me to reevaluate previous thoughts on the owned SUT's; a relegated model is now the go-to model for this Phon', totally unexpected that outcome.