Sennheiser HD 280 Pro, yea or nay?

For some time now I've been using a set of Sennheiser HD 280 Pro headphones, so far I've really loved them and I'm thinking of upgrading to a set of Meze Classic 88's. I can't do open ear because even though the sound stage is lovely it defeats the reason why I use my headphones. I'm using onboard sound so I was wondering if the Sennheisers vs the Meze's will make any difference or if I could get a different set of cans.

i have the 380 pros and the 280 pros... theyre great

The Sennheiser HD280 Pro's are what got me started on my audio journey in the headphone arena. Great set of cans, and could easily recommend them for how cheap they are. One thing to note though, is that the HD280's were actually a little bit harder to drive to the same volume as my HD558's. The 558's have a higher sensitivity, and lower impedance, which I think are the main factors to this. Originally owning the 280's, the lower volume of onboard sound and lack of punctuality in the sound is what originally let me to getting a headphone amp. It works, but it isn't as good as some may claim with those cans.

I ended up getting the HD558's because I wanted open back ones, and at this point, they are really not that much more expensive, and give a superior soundstage to the 280's. The one big advantage to the 280's is that they are a very flat response headphone (great for mixing), and VERY isolated. Honestly, they blocked out more sound than many active-noise canceling headphones. Because of their flat response, they are not the most 'fun' headphone to listen to, but where accuracy is needed, that is what they are there for.

I have no experience to the Meze brand, but looking at the website, the Classic 88's run $250+. For that price, it would be wrong to compare them to the 280's. For $250+, there are a LOT of other options that are probably better. Not saying Meze is bad, but they have some serious competition, and I'm not about to spend money on a brand I never heard of for that much money just to try it.

I've heard some really great things from people about the Mezes and seen them compared favorably to other brands. Most of my available audio equipment lying around was cutting edge in the early 90's so I also want to know if I should go for a new DAC before the headphones, right now the closest thing I have to an external DAC is an old studio grade DAT deck.

I'm planning on upgrading from my 280's to something better and I can't go open back because that would defeat the point of the headphones I use.

Wait so you have the Sennheiser HD280s already? If so, get a good dac/amp like the o2 odac/amp or something of the sort. Like I said, it made a huge difference for me when I went from onboard to a headphone amp. 

Start there, that way you know you are getting the full capabilities of the headphones before you start throwing money at headphones when that may not be the source of the problem.