Strategy for upgrading long interconnect cable run

I am looking for advice regarding the best way to try out a replacement set of long, (6 m), XLR interconnects that run between my preamp and my amplifiers. I am running VAC electronics with a Grimm Audio digital source, a technics sp-10ii turntable, and Avalon Eidelon Diamond speakers.  Most of my interconnects are Shunyata alphas except for this long run, which is (relatively old) Purist Audio Genesis Praesto revision. I am wondering if they may be holding back my system.  Since 6m (5m may work) cables are relatively rare… playing the used market may not be the best idea. I am OK with buying new, in which case I would prefer a brand that allows returns after audition, and/or a brand that does not increase the cost very much in proportion to length (Purist used to operate this way, not sure if they still do). Basically, I am wanting to minimize my risk, but willing to pay if I find a notable improvement to what I already have. I realize there is the cable company… But I doubt they have that many long balanced runs. Any suggestions for which brands to try that might accommodate my needs? Budget around $2-3k. Thanks very much in advance.