If you can't find a PA44, I think that the standard FS Beechcraft Baron is a very good substitute. Pitch/power settings are very similar and depending of course on how well equiped your PA44 is, the instrumentation is pretty much the same too. As for the DA44, it's a nice easy a/c to fly without complex power control i.e. you set a %age power and it works out optimum blade pitch setting leaving you to just worry about keeping it in trim and navigate using the efis type layout of the glass cockpit. So you can learn the instrument part in any of the efis a/c in FS or download a Garmin 1000 addon for any aircraft (search on flightsim.com) and assume that the actual flying will be a piece of cake.. Good luck!