is it worth to invest in a DAC + Amp using 320 mp3s?

pazto,

You are on your way to an amp, a DAC and new headphones. I feel it! 

Then you will play other formats too!

I still use 320 mp3s.  DACs give a slight improvement in sound whether you're using FLAC or mp3 or whatever. I'd get an amp first though, and if you get an amp you really need something to carry the sound over from the MacBook to the amp at line-level quality.  So yes, you'll need a DAC of some sort.

That said... none of your cans really need an amp. 

I'm a newbie here as well, but as stated above none of the cans you have really need an amp (but will of course benefit from one). I think you will be well off with a USB dac/amp. I have a Creative sound blaster x-fi HD which is quite cheap and does give a nice improvement in sound for my Beyerdynamic DT770 pro 32 Ohm and my Sennheiser HD598. I use mostly 320 kbps mp3's as well.

But I think you will have to state a budget before we can really give you advice on a model.

I noticed a very significant change when I got a DAC/headphone amp.  My music is even split between 192-320.  Clarity, sound-stage and instrument separation were night and day.  I'm thinking about digging up the receipt and finding the day I bought my Nuforce Icon HD DAC/AMP and declaring that day a personal holiday.  It's worth it!

There are a couple of things you can try.
An obvious first is to rip a CD to 320 and to ALAC or any other lossless format.
Check if you do hear a difference.

As usual the question is what is the weakest part in the chain.
You might try to connect a headphone to a quality amp and check if you hear a difference due to better electronics.
You can also try the reverse, connect a high quality headphone to your PC.

My gut feeling is that headphones are like loudspeakers.
Often these components causes a lot of coloration and are often the weakest part of the chain.

I'm thinking about digging up the receipt and finding the day I bought my Nuforce Icon HD DAC/AMP and declaring that day a personal holiday.

Classic!

320 mp3 sounds great and playback will benefit from an amp and DAC. but you should consider getting some better headphones before getting an amp/DAC based on that list you have.

that will give you the most noticeable improvement in sound.

Quote:

Originally Posted by pazto 

please provide me an example, I really wonder about what you guys call good headphones (please ignore the bose, they're crap i know)

Those are already pretty good headphones, the Shure, AT and KRK anyway.  The Bose may not really compete on sound quality, but they do active noise cancellation well so they're worth keeping if that's important to you.  I don't know of any other ANC 'phones as good as the Bose.  You can get better sound if you want to spend more money though.  The headphones are most always the weakest link in your chain and usually the best place to spend your money on an upgrade.  Many more expensive and/or better sounding headphones have greater power requirements than the ones you have now and will either not get very loud or possibly sound like crap without a dedicated amp but not all of them are like that.

If you want a new headphone we could help you pick something suitable if you tell us which of your current headphones you like best and why.

I notice that all of your current 'phones are closed.  Is isolation from the outside world important or is an open model ok?

well, you just ordered one of the most notoriously difficult to power headphones around. the K701 are infamous for requiring a very high quality and powerful amp to sound their best.

so you may want to start budgeting now for a great amp. :)