Budget amp / speaker suggestions

Well it depends on what you want to do really. I can't say much, but if you are buying an amp seperate from the speakers you MUST match the speakers to the amp AND the amp to the speakers.

If the speakers are rated for 300watts and the amp only 150, and you push the amp, you will cause clipping and distortion. This is bad for speakers because it is the same as giving it a flat DC input voltage, which heats up the voice coils causing damage and distortion while not adding to the sound.

If the speakers are overrated from the amp, you can cause the voice coil to simply receive too much power and overload. You'd also reach the limits of the cone because it would bottom out and that isn't good for the cone or the ribbing/suspension. This isn't as bad as above, because when the speakers are overpowered you'll know it.

Speakers all have impedeance ratings which are usually matched to the amps ouptut power for a given amount of impedeance. Load is also dependent upon whether the speakers are in parallel or in series connection (because it affects the overall impedeance of the circuit).

Good place to read up is prosoundweb.com if you want.

As far as digital input goes, I have no real idea as I've never used that, but most home equipment will make use of it. As far as pro equipment goes, not so much. You will probably need to convert to a compatible analog signal with the correct gain for the amp first. (IMO the difference between analog and digital in terms of what you can hear really isn't that great, especially if the output is an MP3 which doesn't have great quality to begin with. The main difference really is that a digital signal isn't as succeptible to noise and distortion).