suggestons on speaker cable that boost mid and upper bass

Bigdish, you didn’t mention what your budget is, however Siltech Royal Signature series cables have good bass. Wojciech Pacula noted in his review of the Siltech Ruby Double Crown power cable for Enjoy the Music that they "slightly highlighting the frequency band around 100 Hz". From my experience, the same should be true of the Royal Sig series speaker cables.

Also, the Royal Signature series cables sound warm, harmonically rich, quiet, resolving and very smooth. Tonal color is just right and not over-saturated. Plenty of meat on the bones if you’re missing that with your current wire. Build quality is also superb, though make sure you buy from an authorized Dealer as there are plenty of cheap Chinese knock offs on Ebay. There are a million other cables out there, but I can give them a qualified recommendation.

Thank you melbguy1 for your kind suggestions. Sorry I forgot to mention my budget. I have no experience in Siltech cables, but my budget is only about 6000 dollars, but I would rather not to spend so much if possible, The Royal Signature is just too much for me. I have heard many many good things about Siltech cables. 

YW. Within yur budget, you could pick up a pair of either single wire or biwire Cardas Audio Clear Beyond cables around $4500. Those cables won Stereo Mojo’s ’Maximum Mojo’ award & should give you the qualities you’re after. This biwire pair are new and the guy is also offering free insured shipping in the US & will carry the Paypal fee - https://app.audiogon.com/listings/speaker-cardas-audio-clear-beyond-2-5m-speaker-cable-bi-wire-new-w... I did see another pair of single wire versions in mint condition with free shipping also.

Since you are happy with the highs and design of the Connex, I suggest you research ICs that have the characteristics you seek. Don't dismiss what a change in IC's can add. It could fill in the mid and bass.
Possibly the Cardas Clear Reflection.

bigdish: Cable cannot "boost" mid and high frequencies. They can't add something to the signal. They can, however, REDUCE the bass giving the illusion that mids and highs are more prominent. Best to think in these terms.

Going from a multi strand silver cable to a single, solid core copper cable of high purity might be the way to go. It's been my (limited) experience that even well made multi strand cables impart a lush and pleasing midrange with a lessening of the tone, texture and detail in the lower bass. You can't have it all. Accentuate one aspect of the frequency and other parts can, and will suffer. Balance is the key.

Single, solid core cables seem to do the least harm to the signal and the end result might be what you're looking for.

Also, what lowrider57 says is true. I'd even go so far as to say that the serious coin should be spent on the ICs and once you have that dialed in, the speaker cables would be easier to sort out, provided that you're ICs are up to snuff. 

All the best,
Nonoise

Thank you all for your suggestions. Mich appreciated.  For ICs, I am using Stage III Concepts Gryphone from SCAD to preamp and PAD 25th Anniverary from preamp to amp. Both are great ICs. Thats why I think my speaker cables are the weakest link. I am also thinking of copper wires. Anyone has experiences in PAD and Kubala Sosna speaker cables? I heard they have great density and flow and are a bit warm. Interested in PAD Neptune or Kubala Sonsna Emotion or even Elation. A pair of Dominus are just too much when buy new. Been looking for second hand pairs but not available at the moment. How does Cardas Clear Beyond sounds? 

Unfortunately, there is no one "wonder" cable that will do all of what you want it to do. No magic cable will increase body and musical weight without sacrificing the HF and resolution that you love about your connex audio speaker cables.

You cannot go East AND West at the same time. As cables deliver more musical weight and body, it comes at the expense of resolution, and as resolution increases, body decreases.

I have heard Kubala Sosna Emotion and many versions of PAD cables. Yes, they will provide the body and punch that you seek. However, they will not provide the HF and resolution of a silver cable.

You pays yer money, you makes your choices.

I’d return back to my original suggestion; Siltech Royal Signature series. It might be possible to source genuine dealer demo cables at good prices...particularly after CES.

I like Stage III for power cords, only.
Keep me posted & Happy Listening!

Jmcgrogan is absolutely right, his view has been my experience with many cables - it would take a full page to list all the cables I have owned and tried in my system.  Melbguy's suggestion sounds interesting - that is one cable I have not tried.

I have had full looms of PAD and KS.  I had venustus, corvus  IC's and for SC I had proteus provectus.  Had them for a long time (for an audiophile) but over time I found they did not add the body I was seeking with my Thiels.  Currently using KS Fascinations throughout and they seem to be a nice match as Thiels do not need help in the upper frequencies.  Considered Emotion but not sure you get that much more for the huge price difference.  I believe you get more at the frequency extremes but again, do not think I need it in my system.  

If you give KS a shot you probably want to start with Emotions - they have a good audition program and allow trade ups as well.

Stealth V14 works for me.

Thanks pops. I would also like to try Kubala Sosna cables. :-) What's the differences in sounds between KS and PAD in your opinions?    
   
Yesterday when I tried matching different power cords with each components, I found out that a silver power cord of mine plugging to a word clock was the problem.....  When I used a copper power cord on the clock the sounds were much more natural, though I definitely still want more lower mid and upper bass.    
   
Thanks ebm. Stealth V14 is just too expensive to me.  
   
Thanks jmcgrogan2.   

  

Bigdish, in my system PAD was more revealing than the KS Fascinations.  Not tipped up just more upfront and more detailed which over time became a nuisance with my Thiels.  That applies to the Provetus SC, which has been DQ'ed, and especially the Corvus IC.   Not sure solid core is the best option for Thiel.  The Corvus was PAD's entry into more revealing and detailed cables.  The highs were way over the top for me.  The Venustas on the other hand was the most balanced of the 3.  I ran a 5 meter IC between my preamp and amps.  I still have it but it is currently on the bench.

The KS Fascinations have a more laid back tone with a richer midrange, the Vensustas comes close in this area.  They are ultra smooth with a little rolloff in the upper frequencies and are more dense in a good way.   They also have a well defined bass, I wouldn't mind a little more definition in this area.  My bet is you get more of that as you move up the line.  They  remind me of Kimber 1011 and 1016 without the slight grain you get with those cables.  The real surprise when I went with a full loom were the PC's.  They work nicely on my amp and phone preamp.  They do not add too much bass and midbass which is my biggest complaint with aftermarket PC's.  Hope this helps - good luck.