I had both HD555 and HD380Pro (still own HD555, while sold the 380s a long time ago). If you want to enjoy music with the headphones, HD380Pro is most certainly NOT for you IMO. It sounds very dry lacking smoothness and with a rather severe upper treble roll off. It may be good for monitoring vocals because its midrange is very forward, but when trying to enjoy music, I found the forwardness to be very irritating. Often the singers sounded as though they were screaming in my face - not a very nice feeling. The bass is reasonably tight but the upper bass is recessed and so drums sound a little thinner than they should. A good amp can perhaps fix this issue. Low bass is represented well, but overall the low frequencies sound quite unnatural on the HD380s IMO. The most weird part is the soundstage though. It's VERY wide, but also extremely upfront. This results in a very strange feeling when listening to music although if you like Grado, maybe you'll find this presentation to be OK. What this headphone is really good at is reproducing detail - micro-detials are heard especially well. Dynamics are also great. But these qualities don't help much for making these a good audiophile headphone unfortunately. It's strictly a studio can IMO.
HD555 sounds a lot more musical, even and far better extended in the upper treble to my ears. The soundstage is not as wide as on HD380 but it's got much better depth. Detail is not as good, but HD555 more than makes up for it in musicality and smoothness IMO. There is some emphasis on mid bass and the overall sound can be considered colored and not particularly suitable for monitoring, but for enjoying music, HD555 is nice fun headphone unlike HD380.
If you need isolation, I would get Shure SRH840, if you can find it at a good price there in Portugal that is. It sounds like a combination of HD555 and HD380 - it can be used for both monitoring and musical enjoyment. Overall though, it's in a league above HD380 and HD555 though, so if you can fine one at a good price, go for it. You can also take a look at Shure SRH750DJ, if you need a headphone that sounds comparable to SRH840 (with a bit less treble) and is easier to drive from weak sources like portable players, but it doesn't quite have the isolation of SRH840 from what I've read.