Several of my reds have pH's around 3.5 or so and TA's from 6.5 to
7.5g/l. They are 10 months old and have not yet been cold stabilized.
Tastes are tart but OK with the exception of the amarone (TA 7.5)
which is tart like a lemon. I'd like to reduce both TA and pH in all
of these reds.

Should I just cold stabilize or reduce acids with KHCO3 for example
and then cold stab?

Also, different sources suggest different ideal TA's for finished dry
reds. Pambianchi on page 83 suggests 4.0-5.5g/l. Don Buchan's
excellent FAQ site http://www.malak.ca/rcw.faq suggests 6.5g/l. I
know taste is the ultimate authority but what should I be aiming for
here?

How does one reduce both TA and pH simultaneously?