Much better MM cartridge than Shure V15 IV?

Good idea...get a few hi grade vinyl releases before anything major...a tube phono pre would be nice addition...the more I think of it...there is nothing blaringly wrong with your system...a sub would add oomph but dont expect miracles

Phasecorrect, thanks for affirming my choices so far. Clean vinyl ....yum!

Your point about subs interests me. The matching LS3/5a bass units sit underneath each speaker and act as a speaker stand. As far as I understand the specs, they dig about 20HZ deeper than the speakers alone, down to 50HZ max. Is that a very light addition to the bass response of my speakers? The cost is quite high: $1500 to have the units purchased and shipped to the USA. Does that seem like money well spent? Phono amp a better idea?
Thanks

I'm not familiar with that product...but 1500 will buy you a very good dedicated sub with greater bass performance...rel, velodyne,etc...however if u don't listen to bass dominant material...be aware a goof sub will offer very subtle improvements

Respectfully disagree with Pasecorrect's otherwise good advise, re the addition of a good sub. A properly integrated sub will retrieve hall information/ambience in good orchestral recordings now missing due to your main speakers' limited bottom end extension; even if the recordings are not "bass dominant". It will also (partly as a result of the new-found hall info) improve imaging. The LS3/5a's are a perfect candidate for use with a sub such as a REL Strata. IMO , the improvement will be anything but subtle.

That's fine...Sumaato will have to ultimately decide...most musical reproduction is midrange reproduction which the ls 3/5s Excel at...I ended up selling my sub...but my mains at the time went lower than 3/5s...so I didn't gain/miss much...miles do very...some swear by subs...others not so much...worth a try though