A great interconnect between Soulution 751 and 725

Buy high end used. AudioQuest Wel balanced for example. They were top of the line 5 years ago and are now priced at a 75% discount from original prices. In my opinion, it is hard to go too wrong. 

Albert Porter uses Purest. Give him a call or contact at Porterhouse Audio. 

Your products certainly deserve top-tier signal cables.  There are plenty of excellent options, as suggested above.  From my own experience, and thus my recommendation, is the new Audioquest Mythical Creatures series.  I had Audioquest Earth signal cables (no slouch as a signal cable) and upgraded to the new Thunderbird cable.  I found an immediate upgrade in quality of musical presentation.  However, I waited for several weeks of run-in time on the cables, then switched back to the Earth cables, making certain about what I was hearing.  I definitely could tell the difference and they didn't stay there for very long.  Switching back to the Thunderbird delivered on SQ, once again.  You can find many reviews on these new cables, providing far better description than mine.  All of them are overwhelmingly positive.  Best to you on your journey.

Used Nordost Tyr 2 XLRs in your price range. Great detail resolution and clarity without any harshness. You want something that would let these components shine and this would be it.

Why would you buy a top-notch Soulution stack and then cheap out so massively on cables? 

Go with an Ansuz Speakz D-TC Gold Signature, or just sell all your Soulution gear because you're definitely not hearing what it's capable of.