What is a good pair of studio mon speakers (powered speakers) with a decent subwoofer?  I've got Rokit 6's and a Cerwin-Vega subwoofer, but I want it to sound like a hi-end stereo system, and I want to be able to turn it up loud.  I'm pretty sure it's the subwoofer I'm not loving..any advice would be much appreciated...  

If the subwoofer's got a downward-facing speaker, that's best for watching action movies but not so great for monitoring.
 
But it may not be the sub's fault. More likely, it's the acoustical characteristics of your room and where the speaker is situated within the room. I'd strongly recommend reading Dr. Floyd Toole's excellent book on the subject, Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms. I've found nothing better to explain why subs are such a royal PIA, and what you can do about it.

Good point.  And it's probably safe to say I won't be happy until I have my gear set up in an acoustically-treated room.  It's actually not a bad subwoofer - I've got the woofer facing forward and the vent to the side.  But thanks for the link - I'll definitely look into it.

The thing is a hi quality home stereo system, and a hi quality studio monitoring system are 2 different things. Home stereos always expand on certain frequencys to satisfy what we think we like to hear,  a perfect studio monitor should be flat and accurate. 
 
If you mix on a home stereo your mixes will sound awsome on home a stereo but suck in the car or earbuds. 
Lot's of people like to proof mixes on both studio monitors and other common systems. So a second or third set of monitors is a good idea.. But you will need to sort out which type your after. No point in having 2 sets that are just a little bit different. That will confuse your ear training. You want to work with your monitors for many long hours to get the full benifit of what they can do. 
 
Along with my NMS10's I have my PA and a little set of plastic 4" Panasonic boxes I can flip on or off. I have a Yamaha sub as well but use it like the little speakers only durring mastering to quickly check the low end. So my 3 sets or monitors are radically different
 
I find because I've  been working with my NSM 10's for so long that  my most enjoyable listening experiance over all is in the studio. I'll pour a drink and turn on the sub and sit back and enjoy my work. (Making notes)  
 
I then go somewhere else as changing rooms is also important..to the living room: ( with second drink)  
My stereo system in my living room has these Mission speakers and a JBL sub. Sounds nice there but overall the mix will be off compaired to the NMS10. But some detail like hi hats sounding harsh might need to be fixed. Those hat need to sound good on all systems.
 
Then off to work in the Sunaru ( coffee now) 
In the car it sounds nice but missing detail and with the road noise you might find your background parts are up and gone.  The main thing is the songs should sound good on all the systems and that you can hear each part clearly and at all volumes and even in bad environments with background noises.
Very few people will be sitting like I was in my studio with good playback. 
 
So mabey what you need is a more accurate set of monitors first.  and then a good home stereo too. 
If you want loud, a set of powered PA speakers cannot be beat. Great way to see what your tunes will sound like in a club! There are many 8" and 10" PA boxes that sound awsome these day's. I have a set of 8" Peavey's and 12" Altos and a second Yamah sub. 

I know exactly what you're talking about...So much of it is trial and error...Thanx for the thoughtful responses!

I got the book via Kindle, and I could only concentrate on parts of it that pertained to me...After pulling my own hair out, I was all ears...Very helpful...Never been in the studio except once when I was 19 going to Berklee...I arranged a visit at Blue Jay studios in Maynard...and the guy there was very cool...and there were people passed out on the floor in the lobby...it was 78' I think, but I appreciate the interview...
I've worked the problem with my subwoofer and have 2 questions:
 
1.  I was listening to Europa by Santana on the system, and I couldn't help but notice the vast tonal differences...with the subwoofer at about 68%, between bass notes and guitar...but it sounded right...and it sounds right on my stereo system as well...So I have the question:  When producing with a subwoofer, how much can you trust the mix to sound right with a pair of Polk speakers without a subwoofer...I mean, am I behind the times?  Do I need to get a subwoofer for my stereo system in order to be at market standards?
 
2.  The best speakers I've heard are Klipsch...but when I was living in Montana, I visited a custom hi-fi store, and there were stereo speakers made out of maple, oak...solid wood...15" woofer, 10" woofer, 5"/2" midrange and tweeter...they were about 6' high and shaped like pyramids...Where can I get a pair of speakers like this?  Seems like really hi-fi stereo systems are very hard to find these days.  :)
 

There are cinema speakers by Klipsh that are rhomboid or whatever.
 
We used to have some nice wood klipsh speakers and a Mackintosh tube speaker in the electronic music room at my college.  And a EMS VSC3 someone skipped out with.