Hey, everyone! So right now, I have several questions (following statements) for you guys.
 
1) I currently have the line-out of my pc's sound card plugged directly into the line-in of a stereo player, which routes to a pair of L/R speakers. I suppose anything is better than nothing, but is this wise at all? (Let's assume the speakers are EQ'd)
 
2) I've heard that using headphones for mixing is not the best option for mixing. What do you guys say?
 
3) Piggybacking on the last question, what are the best options for low-cost headphones and monitors?
 
Thanks, guys!

Given the choice between monitoring through a home stereo and a good pair of headphones, I'll take the headphones. What you want is a flat response so that the speakers aren't coloring the sound. Another option is to get a pair of powered speakers designed for recording. Below is a link to a Sweetwater.com page listing active monitor speakers. If nothing else it will give you an idea about what is available and how much it costs.
 
http://www.sweetwater.com/c405--Active_Monitors
 

I use a home stereo for my monitors and I think it's okay. I have the eq set flat and no bass boost or other "enhancers" enabled. I'm using a pair of Yamaha home theater speakers. I also have a passive 12" sub. I get mixes that transport well between different systems. I've been using this system for probably 8 years. It has limitations - it doesn't have a real clear stereo field for example. But I feel that by listening to reference material for years on the same system (played from my PC through my same audio devices), I've come to know how material sounds on it and how to (try to) get that same sound.
 
I used to use a Tannoy system years ago (PB-8) and I know it was a much more accurate system but I think the biggest thing is, at the beginning anyway, to learn the equipment you've got and how to make your tracking / mixes sound like comparable production recordings.
 
I don't use headphones for much of anything except tracking. I have Sony MDR 7506's which I think are pretty good, about $100. I've also got some headphones from MonoPrice.com that are very similar sounding which I use for tracking, about $23 (id 8323). I read about these in TapeOp and had to try them.
 
BTW, if you don't get TapeOp magazine you should - it's full of great info and it's free!

I may be in the minority, but I think the cost difference between a suitable pair of headphones for mixing and suitable pair of monitors gives a slight advantage to headphones.  The Audio_Technica ATH-M50 is $159 well spent: http://www.amazon.com/Audio-Technica-ATH-M50-Professional-Monitor-Headphones/dp/B000P62ND6/ref=sr_1_6?ie=UTF8&qid=1373424339&sr=8-6&keywords=audio-technica+ath-m50
 
They are no substitute for a good pair of monitors with a flat response and well treated room, but may7 give better results than your very likely colored home stereo loudspeakers.  There are definitely issues with mixing on headphones, but IMHO they are outweieghed by the fact that $159 will likely get you a set of weak, plastic monitors that are glorified computer speakers.
 
 

First, you gotta do with what you have to work with.
 
No stereo speakers are EQ'd..... well they are but the proper word would probably be "Biased".  Most home stereo speakers are specifically designed to accentuate certain frequencies..... normally bass, and highs... they have to "sound good" to have people buy them.
 
We, however, don't necessarily want good sound, we want truthful sound..... or as much as physically possible given speaker size and design.
 
Mixing on cans..... vs reference monitors.  Use both if you can. I have mixed a few tunes strictly on cans,,,,,and a $30 pair of Yamaha's at that. The mix was pretty good.
 
It all comes down to one thing. No matter what you mix on, whether it's a pair of walkman ear buds, nice home stereo cans, mid priced reference monitors or top of the line (whatever that may be) studio reference monitors...... you have to learn the gear and the room to have a good mix result. The more you understand that aspect ....and the art of the mix itself, the better your mixes will be regardless of the monitoring means.

Answer:
)1 Ya you can do that, but EQ'ed ah, well, unless you have a 27 band equalizer (1/3 octave) and a test CD to measure frequencies with a sound level meter (Radio Shack use to sell one) and even with that it will still be subjective from the mic that picks up each frequency in the sound level meter, then the human ear chart for frequencies and loudness at which is played and anything else that is included before it suppose to sound good to you.
2) Ya, you can use headphones, I find ear buds to sound better than same priced headphones.
3) Your pick at the store, I like JBL, and since I do not have active monitors supposedly made for hearing (with correction built in like the two-way JBL monitors at $1559 for a pair)
http://www.sweetwater.com/store/detail/LSR4328Ppak/
 
I usually end up mucking it up, but listen to the stereo, headphones - and ear buds, and computer speakers and still muck it up, but I am learning and hanging around here found out some things I did not realize I had before. (like my RME unit has a Digicheck which shows the frequencies as they are playing coming out of the computer which I should have been using all along and probably should correct anything I have done, but there is always the next song I guess.
 
Live and Learn.
I figure none of it is perfect and since I done sound checking since vinyl days (sound level meter) that everyone hears different, every system is different, and all will sound different, but if it sounds almost alright through everything than I guess that is closer or as close as I may get even having the option of better equipment, unless someone wants to build me a $million dollar something or so studio like this one - Blackbird Studio C perhaps:
http://www.youtube.com/watch?v=exQRfHbSwn0
 
and that is only one of the 4 studios there.
 

Also don't forget to check out the VRM box if you have to mix on cans. Paired with a good pair of headphones like the ATH M-50's I think it may be even better than mixing on monitors in an untreated room, especially for the low end.