The PCM-M10 will give you an accurate playback of your input. So will similar units from Edirol, etc., but the PCM-M10 beats them in battery life.
Your current unit might even be decent, but I don't know if its mic jack is mono or stereo--you'd have to try it with a stereo mic. (Actually you could test with your earbuds, which will work as very low-fi mics--just plug them into the mic jack and tap separately on the right and left buds to see if you have stereo.) You also need to see what its actual frequency range is for recording. Its built-in mic is probably made for the narrow band of speech, but it may actually record the complete human spectrum of 20-20,000 Hz.
Assuming that your current recorder has a mono mic jack or lame frequency response, the PCM-M10 is a good choice.
Its built-in mics are actually quite good built-ins for affordable gear. But they roll off steeply under 80 HZ--about 2-1/2 octaves below middle C--and because they are so close together, they don't give super stereo separation, though there is some. Also, there will be handling noise if you are holding the recorder, but it does have a tripod mount so you can be hands-free. Your first step could be to get the recorder and try it with the built-ins to see if it satisfies you.
External mics will be better. Sound Professionals,
www.soundprofessionals.com , has a lot of good affordable mics--even their BMC-2 at about $60. (Don't get the BMC-12, which are spec'd wrong on the website, and are very bass deficient.) A lot of people here also like Church Audio mics, a little pricier but not a second mortgage.
http://taperssection.com/index.php?topic=86896.0Incidentally, some of the easiest affordable mics to find, by Sony (DS70P), are pretty awful. Bad fidelity, noise. Just say no.
The big problem in recording classical music is that because it can get so quiet, you need a mic that doesn't add too much noise of its own. Lower-noise mics get expensive fast. Noise also comes from amplifying the mic signal. There's a preamp built in for the PCM-M10's mic input, and again, it's high-quality for the price, but an external pre-amp should be quieter.
Look at your budget and don't drive yourself crazy. Yes, you can get thousand-dollar mics, but I have gotten some very listenable recordings with BMC-2 and a 9V battery box into the PCM-M10's Line-in input. (You can get the bare-bones one from Church Audio for $40--you don't need high-pass filtering for classical music) The Line-in bypasses the preamp, using the extra power from the battery box to give you enough signal.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250648957070&ssPageName=STRK:MEWAX:ITYou might even be able to get away with just mic to Mic-in.
Start with the recorder alone. If that's too lo-fi, get some mics. And if that's too lo-fi, go for a battery box or preamp.