Jose,
Have you experimented with cabling? I found cables make a huge difference in balance, specifically in the range you describe, as well as the mid-treble range. When I recently switched to Clear Day Cables Solid Core silver cables on my mids and highs, the sound balance warmed up quite a bit, and when I went to very heavy guage (around 8 ga.) long grain o.f. copper on the woofers of my RM30C, the midbass came up quite a lot- dramatically so. The overall balance after those 2 changes was a total revelation.
On the 626, the midbass and lower bass is improved hugely by use of a baffled stand, as B recommends.
BTW- Congrats on the review, Bryan.