So by lacking resolution what exactly do you mean?
Do your mixes lack imaging (front to back the sounds have depth and position) ? Is there muddiness?
What's your room like and your monitoring like?
Are your speakers well de-coupled from the stands?
Are they away from the wall?
Do you have any bass trapping in the room?
You could upgrade your converters and get a small improvement, but make sure nothing in your room is lying to you before you buy more gear is my advice. Room acoustics make a huge difference in the mixing process.
(sorry to sound like an interogator!!)

dw

As they say about computers - garbage in, garbage out.

Please don't misunderstand me, I'm not saying that your work is garbage. But don't, at least yet, blame your DAW. Engineering, mixing and mastering - three very different disciplines - take time/training/experience to achieve professional results. Maybe you should take a look at your technique(s) and your other equipment; how you are getting your sounds into your DAW. (I am often asked to "polish turds", cleaning up substandard production sound.) Also take a look at your plug-in collection and how you use them. It's hard to do a great mix if you don't have great material with which to work.

I moved into the field of audio post production about six years ago, and even seasoned pros have commented favorably on my dialog editing, Foley and sound FX skills, But I still have a long way to go when it comes to mixing. My mixes are solid, but lack that extra whatever-it-is that makes them sparkle.

Brilliant recordings have been made on minimal equipment. Just listen to early Beatles recordings which were done on four tracks.

There is also the "Can't See Forest For The Trees" syndrome, which we all fall prey to now and then. I am always looking for outside opinions on my work. One of my best friends is a very accomplished audio post engineer and mixer, and he regularly rips my work apart; and I do the same for him. And I love flying second chair with seasoned professionals. The mark of a true professional is knowing that there is always more to learn, and being able to objectively absorb honest constructive criticism.

So take a look at your other gear - mics, pre's, etc. - and your techniques/skills before you decide to spend a lot of money on a new DAW. Just having the latest greatest toy does not make a great recording.

Samples would be helpfull here, can you post some?

...

Sorry you missunderstood me, It´s not a muddiness or a misplacement of the instruments in the mix, I already heard this mix in about 5 different studios, the takes are fine as far as the instruments and equipment go , I mean the mix sounds cool, but it´s the same thing as Unclebob says, it lacks a certain something.

I can see why you think I don´t consider my part in the problem, it´s really common to see people blaming the equipment for their bad mixes,but I don´t really know what to do because I actually like how everything sits in this mix. I mean when I took it to the mastering engineer, it sounded just the way I liked it in terms of the mix, but you could hear that the "space" where the sound developed was a bit small, it wasn´t as open as many professional mixes I´ve heard, that´s what made me think of the DAW or the sample rate I used in the recordings, or the A/D converters in my DAW.

I wish you could hear a sample but I don´t have it with me right now, but have you ever had the same problem, when the space isn´t big enough for your mix, could it really be the DAW? I mean it´s not for just any reason that almost every pro studio spends almost 20.000 bucks on an HD system. Are the converters on my DAW a piece of crap or should they give me that something that I need?

file this in the FWIW (for what its worth) department.

Although I mod in the vocal booth here, my expertise is not recording nor do I ever claim to be a "real engineer". I know what those people who I respect can do.
I was not happy with any of my mixes until I heard the "wonk" created by mid level preamps used on multiple tracks. When I cleared that problem I discovered the real benefits of outboard reverb tastefully applied instead of bandied about like cheap jewelry.

I'm still no pro, but I can listen to my stuff without cringing and it didn't require a change in DAW or sample rate or investment in a HD system. I've heard great things done with time and energy spent rather than dollars.