Thanks for the reply, i've had the 840a for a few years & love the sound, but i've only been using it in integrated mode, i've recently been looking into USB DAC's as i want to get the most out of my music collection from my HTPC, so now the option of using my 840a in power amp mode has come to light
The DAC im looking at (Audiolab M-DAC) has the option to use as straight through DAC or as a pre, and it comes with a remote which can control track skip/back/pause/play on the HTPC through the USB, and of course volume level, which would be a godsend because the remote for the cambridge audio is a piece of crap.
I hope it's safe to use my 840a in power amp mode aswell though, i heard it can get pretty hot, it's basically got fixed level input option, so on the 840a you set & save the input level of the DAC to 0db