The watts thing depends. Some are total bs numbers used to decieve and sell black plastic boxes. But others, the good stuff, is usually in some way marked truthfully.
The digital part is a non-issue if you use a dac.
My marantz is plug and play with my computer same as the Yamaha. Both take the LR RCA cables into the Aux port simple as that.
If there is no stand alone DAC in your system, then the soundcard, cd player or ipod, all have a built in DAC that does the conversion, still feeding an analog signal to your amplifier.
Luckily my only modern unit(the Yamaha) has a fairly nice phono section for what it is.
Im preparing to rebuild/mod my Marantz 2245 phono board with some nice quality components, upgrading and replacing caps, replacing a few key transistors with a nice matched pair and new high quality diodes.
We shall see how the Yamaha stands up to the Marantz with vinyl after the operation.