As everyone has pointed out, a properly glued joint is stronger than the
wood it is made off. You can verify that by breaking the scrap you get when
you even off the end. It is plenty strong, and never breakes at the glue
line. Biscuits are primarily for alignment; which is extremely important
for panels as big as you are making.
But, biscuits add considerable strength to the joint, as you can verify by
making a panel and gluing nothing but the biscuits. The result is also
stronger than the wood. But of course, the question then is why bother to
strengthen something that is already stronger then the wood?
If, though abuse perhaps, you managed to break a glued up panel, it would
break right next to the glue line; my scraps always do. That is because it
has to break somewhere, and will do so at an irregularity. The glue line,
however strong, is an irregularity, and serves as a locus for failure.
Biscuits strengthen that locus and make the whole panel stronger. (and of
course, it is only properly glued joints that are stronger than the wood; we
all do things improperly now and then)
As anyone who has taken mechanical engineering knows, the entire strength of
a beam lies at the top and bottom; the inside only prevents buckling. By
placing two biscuits together you get them closer to the top and bottom, and
so maximize their effectiveness. Just besure to let everything dry
thoroughly before sanding, as biscuits near the surface can telegraph their
location if you sand before everything is dry.
The one thing you have to watch out for is that a six board panel takes a
while to glue up, and will take forever if you use many biscuits. I will
use extended set time glue when doing something like that. It is also
important to get each board in tight; if you wait until the end to get them
together tightly, the biscuits will swollen and it will be difficult to
crank everything together. Unfortunately, this takes even longer.
Have I completely confused you about what to do? Sorry.