Hey! Let's see if I can answer these questions. I've heard a lot of players that sound worse than the Karma, that's for sure. The only ones I have thought sounded a little bit better have been the Sansa flash players -I have owned an e200 and a Fuze. Obviously, they don't have the storage of the Karma, but they do seem to sound a bit crisper overall. I also remember auditioning a 4th Gen iPod that I thought was on par with the Karma, but seemed to have tighter bass, but that was a long time ago, and maybe it was just the EQ settings I was using at the time.
I think I am a little biased. I have gotten very used to the Karma after 5 years of ownership, so maybe the sound seems a bit dull to me now. Also, I got a bit lazy about the EQ settings, and I almost always leave the EQ off these days. As I think I mentioned, I mostly use it in my car (Through a Blitz audio RCA input and into a pretty basic Infinity stereo system), so I just got in the habit of leaving the EQ off. The Karma's rep for great sound quality is partly based on its excellent EQ. In fact, there is a whole FAQ about how to optimize the settings
here. It really is a great sounding player. probably not the best ever, but great. There are still times I get into my car, crank up the stereo, and say out loud, "damn, this sounds good."
The features of the Karma, I could go on for awhile about. Let me just say that the controls are extremely intuitive, and have an almost analogue feel. You've got the red stick (officially called a "Riostick," but most people on the Rio forums liked to call the "nipple") and the scroll wheel. The nipple is really useful for basic functions like play, pause, etc, but can also be used to navigate the menus. Once you get the hang of the Karma, you will find that you can use the nipple and wheel in various combinations to navigate very fast.I've never seen another player that has two control inputs quite like this, that can do some of the same functions, but also can do their own things. The scroll wheel on the thing is fantastic, and once you learn how to use it for on-the-fly playlisting, most other DAPs will seem a bit weak in comparison. The Karma lets you insert, append, remove, and re-order tracks on the now playing list while listening to music. I know Rockbox does this too, but having used both, I can tell you the Karma's system is waaay simpler and better. Also, you can create an entire playlist on the player and save it, even if it has nothing to do with what you are listening to at that moment. Rio DJ is a great feature too,a nd I use it all the time. Basically, it just makes you a random mix based on certain criteria, like genre, decade, play count, or you can just say "make me a random mix that is 3 hours long" if you want. It's a cool feature, and very handy for me since I keep audiobooks and stuff on there, and don't want every single track of an audiobook coming up in my music shuffle!
Oh yeah, there's the whole gapless thing of course. #1 reason why I bought the player. Gapless really was a "feature" back then. Thank god (and rockbox) that it's more common now.
What I'm telling you here is the same stuff any Karma owner will probably say. When asked "why do you like your Karma," the three things they usually say are "gapless, EQ, and on-the-fly playlists." It starts to sound like rampant fanboyism at some point, but when you use one, you'll realize it's just the truth. in 2004, the Karma did all this stuff other players did not. In 2010, it still does this stuff, and still does it well. At least, the ones that still work do!
Keep in mind here I don't call myself an audiophile. I own some decent AKG headphones (K44's) and some Shure E3 IEMs. I can't say I'm particularly in love with those. I used to use Sharp MD33 canal phones with it (basically they are Sharp's equivalent to Sony's EX71 canal phones, but I always liked the Sharps better until I broke them). If you want to know how powerful the headphone out is on the thing, I looked it up, it's: 55mW/ch @ 16 ohms. 30mW/ch @ 32 ohms. That's pretty powerful compared to other DAPs of its era, I think. And to think, I used to use minidisc players that were like 5 or 10 mW per channel. I can tell you that my AKG cans are 32 ohm, and the Karma drives them to a volume level that is painful! If I had to pick a set of headphones/earphones I own that sound the best with the Karma, it would probably be those Sharp MD33's, or the Yuin PK3 earbuds I recently picked up. These things are pretty mean. I guess you're not really an earbud guy though, are you?
Oh, um, you asked about amps. Right. I don't go crazy with amps, and i don't really know how to talk the way some of these guys on head-Fi do. All I can really say are things like "it sounds good," or maybe a few specific things like clarity or muddy bass, crisp highs, etc. I'm no expert, man. Just a guy who likes music and digs electronics too.
I have not heard much about people using amps with their Karmas. I'm sure people do it. Some people
have to if they've got some crazy high-impedance cans, right? The dock is probably ideal for that, but of course it isn't portable. Anyway, I can't say much about amps because like I said, I'm not really too hardcore about this stuff (and I don't own any phones with a higher impedance than 32 ohms, which is where amping starts to matter more, am I right?). I did pick up a Fiio E5 recently, which I guess is one of the cheapest amps, but it has a good rep around here. The other night, out of curiosity, I hooked it to my Karma (which was set to "fake line out" mode, i.e. EQ off, volume at 29). I cranked a little Smashing Pumpkins and listened with the PK3 earbuds... Suffice to say, I did not notice an overwhelming difference, but the Pumpkins definitely had a little more "balls." Sorry, I'm not the guy to talk to about amps, but if you are into amps, you might be able to get some good advice on this board, or maybe over at riovolution.org.
Well, I hope you found my ramblings useful in some way. now that I've written this long thing, I feel like I should post it on the forum so that someone else might find an answer to their question somewhere in there as well. Cheers!