worth it to upgrade from the ATH A500's to A900's?

I have read everything there is to read about the Denon AH-D2000's and ATH A900's.
Still I want to know if upgrading from the ATH A500's to the A900's would be a significant upgrade.

Could the Denon AH-D2000's be overkill considering the modest source and phones-out I use?
I will plug the headphones straight in the phones-out of a Marantz CD6000 KI.

With the Denon AH-D2000's, which are placed nearer to the high-end, it could simply mean better sound or plain worse sound with the modest source and amp I use?
More details would be fine, but I don't want it at the cost of some fullness, fluidity, cohesion and warmth, which I get with the A500's.
Are my source and amp up the task giving the AH-D2000's what they want?

Thanks!

You're probably right.
I'll post another thread in a couple of days and leave this one bleeding to death.
Thanks.

Really?
I tried it with my previous thread but with no succes.

Edit: Succes!

Thanks for the replies!

I exclusively will use the headphones for music, mainly classical music.
They don't need to be portable so size and weight isn't an issue.
Both Denon's and ATH's are known for their comfort and indeed my ATH A500's are great.
I prefer closed back, because I like to be locked in a sound-scape.

I love the sound of my A500's and to be honest: considering a new pair of headphones is nothing more than a symptom of upgrade-itis (something I never experienced before: I lived with my previous Sony MDR-CD270 headphones for over 10 years without even considering a new pair) and because I can get a good deal on both the ATH A900's and Denon AH-D2000's.

I like the full and tonal balanced sound of my A500's very much and prefer it over the A700's which I found to be brighter, less fluid and with emphasized highs and lows, so I wonder if the A900's character is more like the A500's or the A700's?

Since I mainly listen to classical music I would like instruments to be better defined, a bit more detail, bit more separation but not at the cost of fluidity and cohesion.

I tried AKG K271's which were superior in detail and instrument separation, but lacked the easy-going nature of my A500's.
In fact I never have been impressed by electronics that were supposed to be specifically suited for classical music.
Mostly it sounded too analytical and cold with less than top notch recordings - I want my headphones to sound a bit forgiving with poorer sounding cd's.