I've looked at the specs for both the Fender Passport 150 and 250. Neither indicate the lowest ohm rating (ie 4 or 2). I'm not going to get into a discussion that only one of us would understand, but unless your manual states the power in watts against 2 ohms, do not connect extra speakers to your Passport system, you will fry the amp. You will probably find that Fender offers an additional system of a slave amp and two additional speakers, but you will find that you're starting to climb into total prices that indicate you probably should have talked to a sound tech long before this. But hey, if you're hooked into a Passport, your best incremental solution may be to buy the slave as opposed to starting another more comprehensive system, and saving the Passport for busking.

For the gal who's just starting out, let's be clear. the worst solution is to buy a guitar amp etc. "with voice imput". Guitar amps may serve one instrument fairly well, but they are built primarily to allow hormonal adolesents to find breeding partners while they conduct band practice in the family garage with the car running... If you get even the most basic box mixer-amp (ex: Peavey 560 or 600) and put it on top of a fairly decent speaker, (ex: Peavey Impulse 100, Crate 12" etc) you will, at that moment, have a basic guitar amp with six decrete and balanced inputs and all the processing that implys, plus a much better speaker, at about the cost of most guitar amps.

For the guy with the string band: Get a used box mixer and use it as slave amp to run your main speakers. Most of them can take up to four speakers at 2 ohms per side, whch could give you up to eight total speakers on the Front of the House (FOH) side. Now use the Passport speakers as monitors (or the whole system as a busking rig). The box amp can take additional mics and line inputs, and actually serve as your main mixer. The problem is that, soon you're going to be into the "expensive expansion" range, and "beyond here be dragons."

For the gal thinking of the Passport. It is a very limited, but simple and light system, with matched components that will forever stay in the twilight zone of good sound. If that is all you ever expect to do, then try one out. However, you then buy into never being able to upgrade, except in limited ways. If I were you, I would look into a small/medium sized box amp like the Crate PX700DLX series, the Peavey 600-680's, the Yamaha EMX620, even the smaller and cheaper Nady MPM4150 (Mackies are way too expensive for you at this point).

Get at least one or two 10" or 12" inch speakers and one or two small pole stands, plus cabling and mic cords. Test a Radio Shack 3001 mic ($35 on sale, a Shure off brand) on your system for vocals. You may only need one speaker for your venues at ther moment but the second speaker can serve as a monitor. The speaker poles are the cheapest, best investment for improving your sound, but remember to focus the treble horn at the ear-level of your average audience (for example, sitting). Get a mic stand with a boom which will work for both standing and sitting (tripods are good for one or two people, after that, they start to trip people as they proliferate. At that point, go to counterweighted booms on round weighted bases) Choose flat black over chrome as it reduces the glare of stage lighting to the audience, and reduces confusion in guest musicians who have to see their instrument (like harpists etc.)

I realize that getting individual components is more hassle than plunking down $700 for the package deal, but if you're serious about your musical future, you need to learn the basics of this stuff. It is less complicated than the steps you took to post your message, and will do more to expose your talents than six weeks of practice.

Be advised that there are excellent deals on used small systems traded in on upgrades, or for sale by those whose dreams faded in daylight. The next time you do a gig where they have their own sound guy, put out the word that you need a small system. Visit a local music store that caters to Rock (shudder) musicians. These are the stores where used sound gear turns up, not at a folk oriented outlets. Pawn shops are NOT good, as these folks will try and charge you top dollar for junk, and there are usually no returns if the gear doesn't work.

And speaking for sound men everywhere, if you do turn up a good deal in sound as a result of his advice, there is only ONE WAY for a woman to PROPERLY thank a man...