Both are straight forward and plenty of info in archives as you've found.
2 tips on the B&M (which I'm sure you'll love BTW - I do mine) -
- be careful when removing center console as the sharp edges can scratch the leather seats/e-brake/etc. it's a little harder in the Boxster than eluded to in B&M inst b/c in the 99x's you have the luxury of tilting the seat all the way back.
- once you've installed the shifter, go for a test ride and make sure you shift into/out of all gears before putting the console back in. This way, you can tweak the adjustable links if need be w/out having to rip everything apart again
If all is good, reassemble.
I don't think the EVO link is worth it - especially w/ the SSK. If I recall correctly, I think I even read once that Tool Pants or Loren advised against it. I could be wrong though.
For the rear speakers:
- add polyfil to the speaker cavities (from a craft store or an old pillow). It helps slow down the air flow a bit making the speakers act like they are in a much larger chamber. The guide is to pack it in there firmly but loosely. You'll know when you have enough b/c it won't fall out when you turn it right side up.
- use a fish tape / or dry cleaner hanger to feed the cable thru the passenger side sill and kick panel.
Good luck and congrats on your mods - both are well worth it