Good thoughts, Wade. I also spent many hours getting used to mixing on the BX5s, running mixes to my 4 other stereo systems to check how they transfer. The mids and highs were nearly always spot on, which let me know that I was hearing these freqs clearly. The low freqs, though, were always the kicker. You're right--since small monitors like the BX5s are light on the low end, one needs to mix with that fact in mind. When I added my sub a few months ago, my low-end "guessing" was over (even though, like you, I had gotten quite good at that compensating). Also, because the BX5s have a low-cut switch (at 80 and 100hz), I'm able to stop my BX5s from trying to produce those low freqs that it really shouldn't even think about, which seems to me to help the BX5s to sound even better on the mids and highs.
Either way, the key here is taking plenty of time to get to know new monitors.
I spent literally weeks of evenings trying different pro reference CDs and then my own recordings to know what I was shooting for while mixing with these monitors. Spending a lot of comparison time early on is a no-brainer.
And yeah, I've seen two
pro-mag reviews that have backed your suggestion that the BX5s are better monitors, overall, than the BX8s. Rather mushy lows, scooped mids, and a bit of harshness in the BX8s' highs are the criticisms I've seen raised--although both reviews have still thought that the BX8s are useable monitors. One review (Future Music, pro monitor shoot-out) included both models and gave a significantly higher rating to the BX5s, despite their smaller size.
So get to know those new monitors well, DJ! It's a fun process and your mixes will thank you.
J.