I have to agree with the posts about the room being so important.
As to the subject, I've used the HR624's quite a bit and also the EX66's.
I really think the HR624's are good, accurate, clean, detailed monitors, but...
they produce no low frequencies, really, and you'd pretty much need a sub to even do some rock styles. There's just nothing at all below 60Hz and it seems like there's a slope from about 100Hz on down.
The EX66's I find to be very detailed with EXCELLENT depth. You can really hear reverb and room sound in them that you can't on a lot of other monitors (they have superior depth to my Dynaudios).
They have quite a lot of highs. The first couple times I used them my mixes came out pretty muddy. There's a switch on the back that lowers the wow-factor that they have a bit, but really bring the highs under control. Very easy to mix on with the HF cut on. The other minor drawback is that they have great, deep, low bass, but a little bit of a dip in the 250-350Hz range. That means that it's a little bit difficult to tell if there's a bit of mud at the bottom, and sometimes it's a little too hi-fi sounding.
On the EX66's, you can hear things that you just don't hear on most monitors in a similar price range. They're very good, overall. Great wow factor too.
I owned the HR824's for a while, but ended up selling them when I heard the Dynaudios. I've not regretted it. The Dynaudios are great monitors too. The BM5A's will cost less than $1000. I think the Dynaudios have a little easier learning curve than the EX66's, but I think that, ultimately, you could do better mixes on the EX's.
Just my opinion.