Bypass caps what value should I use.

Chrissain, if you want to dip your toe into rolling caps, you can indeed start with bypassing them as it is very easy to solder them over existing ones. Use the smallest value, i.e. .01 microFarad. The larger value you use, the more you more you are likely to change the design and induced more phase aberrations. Mundorf Supreme is a good start. The Mundorf Supreme Silver/Oil (good to get more sparkle in a slightly dark system) or Silver/Gold/Oil is a better alternative w/o the financial commitment you would have with the Duelunds (and they are much bigger so won't always fit. If you like the progress you should indeed consider replacements in the signal path and power supply section. As I never keep any equipment longer than three years, I never got into phase II so far, having said that, I may consider now for my monoblocks as I am very happy with them.

YES; a bypass is paralleled. Bypass caps are generally just a small fraction the capacitance of what they are bypassing, changing the total very little. They can and will create phase aberrations, however. Better to replace the original, with one of higher quality and equivalent values.

completely bypassing coupling cap is much better idea if you know how.
it's really not clear how you're going to bypass. if you connect smaller cap in parallel than capacitance will add and increase C1+C2.
i guess i should look for books on audiophile engineering?

I have a question first - how do you bypass a cap with another cap? When you put them in parallel (ie like you would to bypass a resistor) you effectively add the capacitance (ie equal to the sum of the 2), which will reduce the highs. To accomplish what you're after you would want to reduce the value of the coupling capacitance.

I have no experience in the realm of hi fi amps, but build/mod guitar amps and the "brite caps" used in those tend to be 100-120pF. I have one amp that used a .01uF in a brite circuit and that was overwhelming. In a hi fi system where you have more highs, this would be compounded i would think.

I confess I don't speak with authority here - hopefully you'll get input from one of the amp gurus here . . .