Best bet is to find a good integrated (I have an MF A5 integrated, but will be selling that once i get my hands on a tube integrated) and a good DAC that reclocks the computer usb signal before sending analog to the amp (i.e. a benchmark dac which I had for about 10 months and just sold). Be wary...too much solid state with digital (particularly computer digital via USB) may come accross as bright depending on your setup.
One cheap approach would be a Trends 10.1 USB to Coaxial interface device that you plug your IMac into (I've an IMac as well), feeding any reasonably priced DAC of your choice (many great ones for $300-$500) and then connect that into an integrated of your choice (or your current amp/preamp). Key thing is to either get a USB DAC that has a good digital clock on board, or get a good usb interface device that reclocks for you (anything from the trends up to an Emperical Audio device like the Turbo-3, which is pricey). If you don't handle the reclocking, you'll end up with pretty bad sound.
One cheap approach would be a Trends 10.1 USB to Coaxial interface device that you plug your IMac into (I've an IMac as well), feeding any reasonably priced DAC of your choice (many great ones for $300-$500) and then connect that into an integrated of your choice (or your current amp/preamp). Key thing is to either get a USB DAC that has a good digital clock on board, or get a good usb interface device that reclocks for you (anything from the trends up to an Emperical Audio device like the Turbo-3, which is pricey). If you don't handle the reclocking, you'll end up with pretty bad sound.