What monitors are you currently using? If you happen to have top-class passive monitors then an amp would be the best way to go. However, the amp you're sugesting has a lot of bells and wistles on board which you really don't want. An amp has to amplify the inputsignal; nothing more and nothing less. You don't want your amp to "color" the sound. So if you want the most bang for bucks, look for an amp with only an on/off button and a volume control. (all the money goes to what you want, nothing to things you don't need)

If your speakers are regular hifi speakers, then active would be the best way to go. Amp and speaker are designed to match.

See how far you can stretch your budget. Then go to a well sorted store and test the monitors that are in your pricerange. Take a couple of reference cd's with you (music you are really familiar with) and take your time.
Remember you're not looking for the nicest sounding monitor. You want the ones that reproduce the music as acurate as possible.

When you finaly have your new monitors in your studio be sure to get to know them; learn where they boost or cut frequencies.

Good luck and let us know what you decided on!

Mike
www.mikewever.nl