I also use a Garmin Oregon 450. The easiest way I have found to deal with PQ's is to do the download, then unzip AND open the GPX file using "GSAK" (Geocaching Swiss Army Knife) which is a free download from the Internet . You only need to install GSAK once on your PC.
Various databases can be setup within GSAK or simply use a single database for all downloads.
Once the GPX unzipped file is in GSAK it's a simple matter to send all waypoints etc to your 450 by the USB connection cable.
I am not aware of an equivalent application to GSAK for use on a Mac or an iPad. Wouldn't be much good on an iPad anyway as there is no USB port.