Switch to silver for a treble boost?

Carl109, you might also try something with a Teflon dielectric (e.g. Kimber 4TC or 8TC) or no dielectric at all like Anti-Cables.

The way you describe the effect that silver wires had in your system is perhaps consistent with my experience in hindsight. I was incorrectly attributing increased focus and resolution in the higher registers with adding sizzle and "sparkle". For me, more resolution is good, while more "sparkle" is only good if is also balanced with the rest of the spectrum, accurate, and doesn't come at the expense of added sibilance.

Ultimately, a change in gear to equipment that favors the upper registers may be in order for you. Focal, Totem or some other speakers with a bright finish may be the ticket. The English love their mid range, and B&W 600 speaker line, while not as mid range heavy as some, are not as hot up top as some others either.

You mention the 'blanket over speakers' sound. Perhaps it is not due to the cables but to their placement. Tried maple stands? I have padding/carpet over concrete slab and used 2 1/2" maple w/ brass carpet spikes for my spkrs and what a difference. I purchased a workbench from Sams and used the maple work surface to homemake 15x12 platforms for my floorstanders. Have plenty of the wood left for amp stands. Puchased some brass spikes from PartsExprs and t-nuts...bargain upgrade. Not huge...but audible for the better on music/video.

I have short steel stands (short to keep the tweeter at ear-height when seated), which have four brass spikes. Each stand then sits on a cement paver, which in turn is on my timber floor.
The cement paver was an attempt to isolate the speaker from my wooden floorboards and reduce the floor resonating with the bass, which worked.
I think the treble issue is more to do with my compromised hearing sensitivity at high frequencies; if only someone had told me to wear ear-plugs when I was younger and playing in rock bands! Oh well...

If you really want to change the stereo's sound then change the Stereo. The whole kit and kiboodle.
Use an old all tube pre with out of controll gain like my ARC (idle for now) Then employ a class D switching amp like the 500 wpc Spectron III its got digitistis in a minor key only. Then Spend a few bucks on using Silver lace cables from Home Grown audio. They are not really in the same league as Signal and I own both.
Finally make the funeral arrangements for the Maggies get a spine and just let it go. Then buy some enormous German horns that sound like a razor. No blankets just nice clean Avant Garde Trios the German horns. Hide the Maggies elswhere for a year or two or else you go back to Momma.

I didn't read all the posts so I don't know if this was mentioned already. If the 602's have dual binding posts, try getting rid of the brass jumpers. Make your own with a couple of short copper pieces. Second, run your cables into the tweeter binding posts and let the jumpers take the signal to the bass. At the most these will only help a little but it's FREE and every little bit helps. Good luck.