Cary SLP-05 balanced or single ended

I purchased a Cary preamp and read in Stereophile that the performance in balanced mode suffered compared to to unbalanced mode. Of course this leads me to look for RCA type interconnects. I'm a DIY guy to a point and was looking to build my own, rather than shell out large sums of money for brand name interconnects which I'll no little how they sound until they show at my doorstep.

VH-Audio sells some very nice silver wire with a cotton dielectric and low capacitance sleeve. I'm thinking of giving this a go. Any thoughts?

The detail and excitement this tube pre brings is amazing. There is a cost however in that some songs portray highlights a bit over the top. The same goes for vocals where is can get a bit shouty. I tried some brown base Sylvania's yesterday and that cured the upper end aggressiveness but at the expense of some detail and loss of lower end textures in the base/midbass dept. Is there a happy medium for 6SN7 tubes in this regard?

FWIW, I'm fairly new to tube based equipment. I'm hopeful for some insight from some well experienced folks here.
Thanks much!