After seven years of not really liking most GPO sounds, and complaining here occasionally to no avail, I figured out the answer to why others like what they hear but I don't.
I bought better headphones. There is no longer any question in my mind that headphones are one of the most crucial elements in a GPO system, assuming that you rely on phones for part or all of your monitoring.
I've mainly been using the AKG K240DF, a classic professional studio phone, which was recommended here when I started. Even the estimable Dan Kury uses and recommends them. I sneakily disregarded his well-meaning advice to keep them, and received my new top-of-the-line AKGs today.* They make an absolutely amazing qualitative difference, even with no burn-in, though the K702 is said to require as many as 3-400 hours before they fully open up.
I hooked them up to my modest headphone amp, a Presonus hp4, into which you can plug 4 cans simultaneously. My trial pieces are early music arranged by by me for modern orchestra. I have never been satisfied with the quality of sound from my samples and have been trying to figure out whether the problem is the GPO patches or some element(s) in my hardware chain from soundcard to headphones. Violins often sound scratchy, unpleasant. Drums are seriously underwhelming.
After the new phones arrived today I started listening with my AKG K240S cans, not much used since purchased new about 6 months ago. They produce a pleasant sound, good bass and general resonance. The piece sounded nice, but a little murky and underdefined. I need to hear the individual instruments better.
Then I listened to the same piece with my K240DFs, which I had bought used on Ebay about six years ago, obviously very well used as the pads were cracked and worn out. Cable and current pads are factory replacements. The DF sound on the piece is a little thin and scratchy in comparison to the K240S. In the DF's defense, I can't get enough power from this amp -- the pot is turned all the way around. Thus it may need more juice to produce. Or, maybe the drivers are over the hill. I concede that there may be something wrong with this individual pair.
Then I tried the AKG K702 fresh out of the sealed box. Ahhhhhhhhhhhhhhhhh. All of a sudden my GPO4 orchestra got bigger, more powerful, and more spread out over the stage. There's the big bass presence I have been looking for, hoping it was there. The contrabasses just asserted themselves. And the K702 is not famous for bass. Haha, mine has it, sorry about yours, LOL.
Another of my arrangements has a lot of timpani and bass drum, which always sounded anemic with both my older phones. Today -- BAM, BOOM! -- the K702 really brings them out. Finally, they produce a huge rumble. Still not nearly like what Dan can do with his stunning sequencer mixes, but I'm pleased with this. For years I have wondered why in the hell I couldn't get any power out of the percussion, ever since I first got Sibelius and GPO in 2003. Now here are the big drums in all their glory.
Overall, there's an order of magnitude improvement in reproduction quality. And my K702 does not even have two hours of burn-in yet. Listener reports on headphone boards suggest anywhere from 150 to 400 hours of burn in for this unit. I look forward to Hour 300.
My low-end amplifier is probably also a factor. A more powerful boutique amp is on the way -- a Sjostrom Audio QRV-07 kit, which I hope will improve things even more. On the hp4 I have to turn the volume dial almost all the way around to get normal listening level on both the DF and the K702.
Finally I can get back to focusing on playing with the musical structure and making more of it instead of tinkering constantly with the software mixer and agonizing about why I am not hearing the beautiful sounds I think I ought to be hearing.
I wonder how many colleagues on this board aren't hearing everything Gary's and Tom's orchestra can deliver.
*The AKG K1000 is more expensive than the K701/K702, but it's a completely different design, kind of eccentric, and appears to be more of an audiophile device than workhorse reference phone for professional engineers or composers.
(Of course I know I'm supposed to use studio monitors to mix, but I don't mix or master, I do What-Ifs with Sibelius. I live in an apartment, work late at night, and would prefer to spend $240 for high-end headphones than $3000 for pro monitors that I can't crank up fully anyway.)