Bel Canto 300iU; DAC flexibility

Hey all! Still kinda new to the community and I'm looking for a little help here. I'm looking to power a set of PSB Synchrony Twos and I'm going to purchase an integrated solid state amp. My number one source is going to be a USB input from my computer (lossless files), but I'd also like an input for a Sonos wirless media player. I'm interested in the Bel Canto 300 iU listed for sale on here as I think I'll need the 150 wpc to power the PSBs. If the DAC on the Bel Canto were to become outdated, can I get an external DAC to override the onboard DAC or do I have to replace the whole unit? I'm also interested in the Peachtree Nova 125 but I can't find one used. Do you guys recommend an amp with no DAC (get a separate for more flexibility?)or find the right integrated with onboard DAC?
Hi Duncan, you may have already made other choices by now. But, for what it's worth, the Bel Canto s300iu is a great sounding integrated. Solidstate impact with tube like mids and naturalness. Offering up a very musical presentation. However, most all USB inputs leave a lot to be desired. I'm using an external DAC ( Arte Forma Fiona - dual mono design ) and a M2Tech Hi-face II SP/DIF 24/192khz ( no digital input on S300IU ) right off my laptop and running all WAV's. And it blows away the usb options. On this device, and most usb dedicated dac inputs. I highly recommend this type of setup for ultimate resolution.