Help with advice for high end speaker cables for my system!


Hello I could use some advice with speaker cable choices.  I am using a Marantz AV-7704 preamp, 2 Krell  KAV250a amps, and a Krell KAV 250/A3 amp.   The 3 amps are running to a pair of Martin Logan Request floor standing speakers, a Martin Logan Cinema center channel, and a pair of Martin Logan in ceiling surround speakers.  2 of the amps are bridged, one each dedicated to a Martin Logan stereo speaker, and the Krell 3 channel amp is running the center and rear surrounds. I listen to about 50% stereo music and 50% home theater.   I could really use some help and advice with stereo speaker cables for the Martin Logan stereo speakers.  All the high end shops in my area seem to have closed, so the ability to demo different cables is apparently not an option.  I am considering Audioquest Oak cables, but really open to suggestions, especially if you have used similar components with good results.  Thank you!!
admiralrobert1
Going to be endless suggestions. MY suggestion is same as ron1219, The Cable Company can assist you if you live in USA, loan you cables for a fee, which is given back to you 100%, as a credit if you buy something, anything, later on.I also personally stick to the low end of the speaker cable game. My speaker cables cost one percent of the cost of my speakers.I use Kimber 8TC. (however I do use multi thousand dollar IC)
My amplifiers came with speaker wire.... off topic... I know....
easy to test the zip cord downgrade theory as you already have the Monster
agree on Cable company - what a great and effective business model
i use a variety of wire: Mogami in the mobile recording rack, Blue Jean and Non-DBS Audioquest in my vintage system, a mix of Kimber and Shunyata at the Condo
100% DBS Audioquest in my Reference system

I would caution you to temper your expectations, expecting a "very substantial" upgrade from your speaker cables is a tall order in my experience. Like Elizabeth, I found money was much better spent by proportionally spending more on interconnects than speaker cables. Again, she and ron1319 offer excellent advice in suggesting the assistance of the Cable Company. 
This is very helpful, thanks.  When you all say get demos from the “cable company” do you mean retailer or manufacturers?  I don’t have a good high end shop in my area.  Do the manufacturers offer these demos directly, or do you have to do it through a retailer?   Also, if anyone has experience with cables between Martin Logan speakers and Krell Amps, that would give me a good starting place (brands) to try.   Thanks for all the advice!
Sorry about the confusion. In USA there is a retail online store actually named: "The Cable Company" here is the link:
https://www.thecableco.com/ 
They only lend cable to customers residing in USA .