Which Component Needs to be Upgraded First

In the bigger scheme of things cables make marginal improvements.Place a high priority on the source.

I owned the ST140 some 15 -20 years ago. I owned the Khorus speakers about 5 years ago. You need a better amp - pure and simple. Updating your source to a better dac would also be a must.

No mention of how much money you have? You can get an awesome DAC today very little money. I think you can do both instead of paying what you might be considering for one.

Get an Oritek Audio modified Zhaolu D2.5 dac for $599 new. It is an absolute giant killer. You can use your Sony for a transport. This DAC is amazing and outperforms dacs cost up to 10X more! You can also sell the Sony and use an Oppo for a transport.

For the amp I would stick with a nice SS or Hybrid amp to control the bass on those X speakers. I own an ART Audio SLA2 that costs only $285 new and it will smoke the once wonderful ST140. This is 200 watts per channel. I can share more if you are interested.

Your speakers can use more midrange and the Monarchy SE160 mono amps would be great for some $1200 or so used. A used Belles Ref 150 ($1400) is also a great amp with better high and bass then the Monarchy. The Monarchy wins out out for mids and wonderful warmth.

Bill

I think it gos a little beyond a simple cable upgrade,a decent conditioner can do much more for a system than a next up cd player or amp.Having that right youll hear just how good that gear is or isnt.I used to say that it was money that could be used better.The building blocks to start with got to be there.Thats my veiw like everybody elses two cents.goodluck

I have found conditioners to degrade sound and limit current/dynamics. I would have to say spend that money on direct 20 amp lines to your room before a line conditioner.
Also get a decent power cord.

I know many differ on opinions of power conditioners, so this is just my experience.