Let me reiterate what Adam and I both said earlier: You can use newer, better speakers with your current unit. Those that say you cannot are not being honest.
I used my current HT speakers with said DPL unit for over a year until I saved a few more bucks and decided on a newer "digital" receiver with all the featres I needed, and the sound was awesome. Ading the digital processing when I jumped for a new, better than BOTL receiver, it just got better.
So, for the best impace, go for five good, matching speakers now, maybe even a subwoofer if you can swing it, and save up for a better than bottom of the line receiver. You'll be glad you did.