The software shouldn't affect power requirements, but the HD and CD definitely will.

If you're swapping things in and out, a close look will probably show a power, or at least current rating on each of the drives. 90 W doesn't sound like much of a PS. 350W used to be considered plenty big to give yourself lots of "reserve'" but they've been creeping up to where that's about standard or even minimum now.

Many of the newer hard drives are higher rpm, and the multi-X CD drives also run at higher speeds, so they do eat more power than the older ones, just spinning the disks.

You shouldn't get noise from the "power supply" itself, but the fans it needs to keep it from cooking can be pretty noisy sometimes. There are "superquiet" fans around, but I can't say whether they're really less noisy of that's just advertising BS. It does sound like you're dragging the PS output down (low voltage), so you probably need a little more capacity. The question would be whether you can fit a bigger PS into your mini box (and whether you really want to go that route).

If you consider putting a bigger power supply in your mini box, you should be able to find "noise figures" as part of the specs, but you may have to dig a bit - and the box itself can affect whether you actually get what's advertised.

If you want a big Hard Drive, and don't want to put in a larger capacity Power Supply, you could consider an external HD. Most of them have their own transformer/converter, so they don't draw anything but "signal" power from the main computer. You just have to find somewhere to put them, and you have another couple of cords to trip over.

External CD drive/burners are similar, but there are some speed limits that need to be observed with an external one. Most of them connect USB, and if you don't have USB-2 you're limited to 12x or less on the nameplate and probably 4x usable. With USB-2 or Firewire, you can probably get useful 16 or 20x performance. It can be a little harder finding a good location for the external CD too, since you have to get to it to put the CDs in and out.

If you have a use for the quiet mini that doesn't require stuffing other hardware in it, I'd be inclined to talk to my supplier about some quieter fans for the big box - at least as a planning stage.

John