Prior to upgrading all my cabling from Wire World (4 Electra 7 @$260, Series 8 XLR @ $600 and series 8 speaker cable @ $1500+, and 2 x 15 yo Boutique PCs @ $500) I applied Mad Scientist Audio's Graphene Contact Enhancer to all of them (ditto to all the new cables). That alone was revelatory, and dirt cheap compared to replacing cables, but I read a Agon forum thread about Counterfeit Chinese Cables and tried replacing just my Pangea Premier SE coax ($169) with a Nordost named brand (only the name is copied, still bad, but...) Nordost Odin 2 from DIY HiFi Store at ~ 1/3 the price + free shipping. The only knock being it took 3 weeks from China to S FL, but it was WORTH IT.
I then slowly proceeded to replace everything with the exception of 2 PCs; one to my CorePower 1800 PLC and one to my Audio Alchemy DDP-1 external power supply both from Amazon < $35! and amazing. The XLR interconnect is Odin Gold as are the PCs to my Audiolab CDT6000 and Tweak Audio EVS 1200 power amp. Finally I bought Nordost Odin 2 speaker cables which I eventually replaced with Odin Gold. All in < $1000
since then, Verifi Audio has introduced 2 products that from the user reports are amazing and relatively inexpensive; the Swiss Fuse and the Puron AC power conditioner (see the Agon forums). I haven't gotten them yet, but these plus Graphene Contact Enhancer seems to be must have upgrades before upgrading cables
hth
