Hi Peter - you have a very nice portable there (wish I had one), but we need to go over a few basics...
1. HF doesn't work like TV or FM. It's largely dependent on the sun, and the time of day you are listening. In general stay below 10 or 11 Mhz during the night, above that during the day. The reasons for this are given in a nice basic site, below (links are blue) - note that you will need your Flash player tuned on
Propagation Primer - Flash Movie by AE4RV
2. I have a feeling you haven't looked at the SW antenna gain switch on the side of the radio. I'm betting the DX position will give you the better signal strength, but along with that...
3. Yes a better antenna will give you a lot more to hear. Get it as far away from the home, and nice and high, as you can. The recent traffic on the PL880 Yahoo group suggests that the PAR EF-SWL antenna works quite well with that radio, and seeing that you are in Washington state (where signal strengths tend to be less), you would have little trouble with overloading issues. Here is one supplier....
Par Electronics EF-SWL End Fed Dipole SWL Antenna. Par EF-SWL.
You will need to construct a jumper to get it to your radio (the typical PL-259 connector used on coax won't work with the 880's antenna jack), but from all indications it works quite well. Of course you can construct your own, and we have several links on that very subject here...
HF Antennas - The RadioReference Wiki
This is just a small sample of the various antennas you could build or get. Many ham related designs can also be used with a little adjustment of the math.
Just about out of room - catch you later...Mike