Phono preamp or SUT for low output moving coil

I don't see why this is a question. There's no problem having enough gain with either tube or solid state with the cartridges mentioned. As long as the input of the phono section is properly designed its plug and play; no need for an SUT.

If you want to use an SUT you have more connections but it does allow you to use nearly any phono section that has 40-45dB of gain, like you would expect for a high output moving magnet cartridge.

FWIW, phono cartridges are balanced sources. SUTs can be configured to accept the signal in the balanced domain and send it out either single-ended or balanced. There are also fully balanced phono sections that are tube and also solid state. We developed the first of such devices back in the 1980s.

Balanced is nice because it can eliminate any sonic artifact brought on by the cable itself.

In my opinion, the Krell phono stages were OK as SS phono stages used to go back in their day, but these days there are both tube and SS phono stages that handily outperform them. Specifically, modern phono stages are in general more free of artifacts that I used to ascribe to transistors per se, a kind of clinical sheen over the music. Modern solid state units have overcome that issue.  Likewise, modern tube phono stages are no longer guilty of narrow bandwidth (droopy bass and soft highs), of which they once were accused, rightly or wrongly.  I'd recommend you (winalovski) consider a new phono stage, rather than to pour money into the Krell in order to repair it.  Of course, I hasten to emphasize that this is only my opinion, but it is based on lots of listening to a wide variety of phono stages.

being an old timer I have old timer equipment and through all these years I got pretty attached to it however, some of it started to give up so I’m looking to either repair it or replace it but to your opinion, I agree that maybe it’s time to go away from Krell to something else, My speakers, they are all timers too🤣 . Martin Logan‘s Monolith from 1986 with newer panels though, And Wilson puppies.. They look like Laural and Hardy. They sit next to each other, and I love to switch between them to different kind of music. For some poor recordings, I have also subwoofer. I love Manolis for classical music. The sound stage is just incredible. For Jazz and some rock music there’s nothing like Puppy. Could be that Krell amplifier will get refurbished to original sound quality, but preamp I’m not gonna bother with it.

As I mentioned before I like the sound of audio research and never heard McIntosh, but for some reason, I like the look of it 🤷‍♂️ if it sounds as good as it looks, I will definitely consider it. Wow, that would be quite a jump. Well, years ago, I was much closer to new electronics high-end. Going to some electronics shows I met Jim Power’s from Martin Logan what a great guy that was unfortunately no longer with the company so everything is changing.  Now I just enjoy my music and I would really love from some of you gentleman to give me some advice. I don’t want to change the speakers that’s the bottom line. I have also good turntable. It’s a Linn sondek LP 12 so I would need to work around these things I hope for some good advice. I would really appreciate that. Thank you so much.

My speakers in a second system are older than yours, Beveridge 2SWs, and the woofers I use with them I built myself in 1970-71. (I am told the original Bev woofers were never very good, and nearly none have survived the 40-45 years since they were made.) the TTs are either a much upgraded Lenco with two tonearms or a Victor TT101, with modified plinth. So I am a firm believer in old stuff.