Upgraded banana plugs

If you REALLY want the best, solder your speaker wire ends to the x/o in your speakers on one end, and the circuit board of your amp on the other.

+2 if you can, no connector.  Can't go wrong.

May I suggest simply a trial of bare wire. 

+1   The best connector is NO connector, if you can use it that way.

May I suggest simply a trial of bare wire.  I had some higher end LAT International speaker cables with expensive locking banana plugs, one of which broke.  I stripped all of the bananas at both ends and re-connected, the sound opened up and improved in every way.

Great responses so far. I never would have guessed something as basic as connectors and binding posts could make such a large impact on a systems sound. I feel humbled to say the least. 

Based on the advice thus far, before changing any components I should get the speaker/amp binding posts changed out and then see where my sound is at that time and work my way up from there. A popular upgrade for the Sixpacs are replacing the standard coupling caps with Jensen paper in oil caps that could bring back some tube magic as well.

Kacz, my Squeezebox does have a volume control so I may give your suggestion a try however I have subwoofer control and tv sound into the LS15. I could try nos tubes in this unit as well. Lots of options but I'll start with the basics first. 

For another upgrade (which is what the new plugs are), replace the binding posts on your speakers and amp with Cardas Rhodium over Copper ones. Brass reeks.

Can I make a huge suggestion? Since you are playing around with things? Does your front end have a volume control in software at all? Not sure with your tube amps will be enough power alone but if you have software volume like on your squeezebox or DAC try taking the preamp out and hook direct to the amps. And tell me if that helps at all. The DAC needs a decent output though and the amps need pretty good gain. But if it does work it's usually magic.

Silver and copper are the most conductive metals you can get. Your last banana plugs were probably brass with very thin gold over them. Brass is about 70% less conductive than copper, gold is 30% less conductive. Which is horrible for an electrical signal. Which is in all the tests I’ve done tend to dull and smear the sound and restrict the signal, and restrict the soundstage. The ones you upgraded to are far far better conductors and pass the signal less intrusively. And what you are hearing is more of the actual signal and sound of your system getting through. Unfortunately you may be hearing mismatches and warts now as it’s more revealing. You probably based your other component matching on what the other bananas sounded like.

I would honestly suggest not going back. I think you should start with the best and move from there. In the end you’ll be rewarded. However I guess that means you have to find other components or change something out. If you’re not willing do do that then I guess you’ll have to go back to the other ones. But keep the new ones for when you do some day buy new gear so you can add it in then if you do any future upgrades.

I changed out all the brass in all my speaker binding posts, changed it out on my amps, and all the RCA inputs. And got rid of it all in my speaker wire ends, and RCA wire ends and use all pure copper now in everything. The sound difference was immense. Absolutely incredible jaw dropping improvement. However it will reveal any flaws or mismatches if you have any and will be very revealing. Mine only got better and never worse with the gear I have. You may just have one piece that isn’t working with the rest of the system now. The challenge will be now to find out which one it is. If you’re up to it. If not, go back to the old worse, bananas and call it a day for now.

My guess is you just got to hear how your system really sounds .

Don't know the answer to your question, but I hear you on the harder, less musical sound. 

I bi-wire and have found that the Cardas binding posts and banana plugs get what you are seeking ... a more musical experience with tube magic.