Lab top or table top

If budget is flexible, check out the CAPS machine from Computer Audiophile founder Chris Connaker. You can purchase it ready made in a couple of configurations at:

http://shop.smallgreencomputer.com/Computer-Audiophile-Pocket-Server_c5.htm

Chris has put alot of thought into parts selection, noise level, etc. to achieve quality sound. Read more here:

http://www.computeraudiophile.com/content/405-computer-audiophile-pocket-server-caps-v20/

I think you need to describe a little more about what you're trying to achieve, and why your iMac isn't cutting it.

If you're just looking for something for music storage and money isn't the primary concern, I'd recommend getting a server-grade machine from a company such as ThinkMate, ZaReason, or Silicon Mechanics. They have stuff ranging from the intro-level / affordable to the huge-business-only machines. I got a small server from Silicon Mechanics a few months ago, put two 2TB server-grade hard drives on it, got it pre-installed with Linux (CentOS 6.2) and it's been sitting in my closet happily running 24/7 since. The hardware on these machines are generally bullet-proof, as they are intended for commercial-grade applications.

It runs (among a lot of other things) my Logitech Media Server that I use for distributing lossless music files to multiple Squeezeboxes throughout the house.

The one I got is this one:

Silicon Mechanics Rackform iServ R101.v4

And yes, you can get these pre-installed with Windows, so you don't have to be a Unix geek to use one. I just personally prefer Linux, but Windows is a perfectly good choice for this application.

Michael

Do you mean LAP top? What's wrong with your I-Mac? Mine has been going strong for 4 years. It has a nice screen and with the upgraded memory, handles a lot of stuff. What other equipment do you use for playback?