floor facing bottom inlets will provide the coolest air possible out of the available air (unless you have a central heating register under your PC or something similar
. the mobo airflow consideration is important. if i was to add the noise of another fan, i'd want to make darned sure that it's flow is optimally configured to cool to it's maximum capabilities. i'd probably use a small diverter on the bottom fans inside the case to turn the air towards the mobo instead of allowing all that cold air to bypass the hot stuff & exit through the PSU. as long as PCI aren't unecessarily blocked, y-not?
jtroutma, what kind of radiator are you currently using? did you make a shroud? it is possible that bad airflow could be the problem. regardless, the BIX should do a good job all by itself as long as proper airflow is maintained. you could probably replace the old one with the BIX. the single rad will reduce your risk of leaks, leave room for other mods, & won't require cutting up the case any further.
BTW, i was thinking it would be a cool idea (no pun intended) to make use of bottom inlets & locate the PC on top of a household central air-conditioning register. if it was sealed well to the register, it wmightn't require fans & the very cold, dry, & dust-free air would make the whole case downright frigid. of course, care would have to be taken that the PC doesn't burn up during the winter or while the AC is not running
