Go to Radioshack and ask them for an inline fuse holder. Get an assortment of smaller fuses like .25, .5 fast and sloblo types. They will know what I mean. The sloblo fuses will allow transient power peaks and will still provide plenty of protection. I use them all the time in my Advents because they don't make parts anymore and I love the way they sound. The fuse is about an inch long and as big around as a crayon. The fuse holder is designed to hold the fuse and make good contact. The holder is wired so that one end is connected bare wire directly to your speakers positive terminal. The other end is connected to the speaker wire coming from the amplifier. You only need one per speaker and it should be on the positive side to prevent damage. You can connect the holders to your speaker wire any way you feel comfortable. I use a plastic wire nut. If you crank up your amp too high the fuse will blow and prevent damage. You can experiment with the proper size so you don't have to change them so often. The fuse holder is held together by a bayonet type connector so all you have to do is twist it to remove and install the fuse. Once you see it, it will be very obvious how to connect and use it. The fuse holder shouldn't cost more than $5 or so.

On the sub side of things, I bought a $100 KLH sub 15 years ago that is still pounding out the bass. While it doesn't go as low as most it still does pretty well in my 3.1 system.