When to change a cartridge?

@inna main instrument is piano and I got into playing organ in bands as a teen. I learned French horn, guitar and a couple others. My sight reading is a little rough, but I did a lot of formal study (orchestration, counterpoint, etc.) when a youth. Only after I quit the lessons did I start playing an old Melodion (sort of a foot pump organ that used reeds) in my parents' house, and got into blues improvisation. The instrument sounded like a big deep harmonica. 

What I do with digital is play files from an SSD, so they can range from redbook standard 44.1 to high level DSD/PCM. I use a DDC (digital interface) that not only isolates the usb input, but also affords an I2S output which is what I use for one of the DACs. It's the best sound I've gotten from digital. I do have a good transport-a C.E.C. TL5, their entry model, but I find the sonics on files running through the above described chain to be very musical. For a long time, I did not like the sound of digital. I only began to appreciate it in seeing and hearing what archival restoration projects yielded. It impressed the hell out of me. It took me a long time to warm to digital. For the modest amount I've invested, the results are unexpectedly impressive to me, a long time analog/tube guy. 

Bill, you are a serious musician.

I wanted to ask you about Lamm amps. Did you compare them with other top tube amps ? VAC, CAT, some Japanese perhaps ? In any case, there must be something very special about Lamm. But you don't use Lamm preamp or phono stage. Not as good as power amps?

whart, I wish I could warm to digital. Perhaps I have not spent enough $ on it. I recently bought the least expensive Moon (280D) streamer with DAC. I compared it against a $9K Linn and hardly heard any difference.

When I put on a record (varying by recordings, of course) it is so much more present than even the best digital. I think the best digital recording I have heard is Patricia Barber's "Clique." It's at least 192 sampling and sounds damn good, but it just doesn't come from an envelope of air the way vinyl does, at least in my system. Again, though, I have put much more money into my analogue front end. 

One thing I do like about digital is that it is smoother, but music, as I'm sure you know, is not always smooth. You said you played the French horn. Saturday I heard Dudamel conduct Mahler's Fifth. Man, that French horn jumped out at me. From my experience, I can only come close to that kind of sound on vinyl.

It is not entirely level of investment... although an appropriate level of investment vs ones analog end is important, and so is the brand choice. I owned Sim for many years... and that is not the equipment you want to be putting up against analog. It is just too digital sounding. 

I also have a lot of experience with Linn streamers and DACs. There are multiple levels of DAC and need to be paired with appropriate preamp / amp. 

But careful choices and investment digital streaming can sound as good or better than analog. 

ghdprentice, what brand of streamers and DACs would you recommend to compare to analogue? I owned a Moon CD player that was fairly expensive and I did not like it at all. It exaggerated the midrange, sounding pretty good at first. It took me a little while to recognize the distortions.