Jimbo21
Just got "Mixing Secrets for the Small Studio" by Mike Senior and right in the first section he talks about unless you have really expensive monitors the low end transients are fairly skewed in that the "porting hinders the monitor's ability to track moment-to-moment changes in the mix signal. Specifically, the port causes any spectral energy at it's resonant frequency to ring on for a short time, and while it's this resonant buildup that generated the port's flattering low-frequency level boost for a constant noise signal, the same quality also adds short resonant tails to fleeting percussive attack noises (transients)". He also points out that "the resonance not only disguises the true decay attributes of the sound itself, but it can also make it difficult to judge the character and level of short duration studio effects (such as modulated delays and reverb), which are useful at mixdown".
So, understand this flaw and be aware of the potential issue. Mix with this in mind. Check on good headphones. Check on different monitors with different resonant frequencies. And you're done.
Notice all pro guys tend to check on multiple monitors in the studio anyway? This one particular flaw doesn't really sound like too big any issue we can't get around. In the end, we're probably better off saving $2000 and spending that on 6 months of good singing lessons. Your songs will sound much better. I've pretty much stopped buying gear now and I'm running off pretty basic stuff - Yamaha HS80m's, pair of Rode K2's (well those are mid/high end), a 58 and in through a UA25-ex. I honestly think that's plenty to get a really great sound if I do it right. I'm now going to invest probably about $2000 in singing lessons as I approach recording vocals for my album at the end of the year. Weak points. Find them and fix them first. Stressing about your monitors not reproducing a few sets of low end frequencies accurately really shouldn't be too big a concern from the overall picture unless you have already fixed everything else and this is currently your weakest point. And you're rich.
By the way, this is not intended to be a flame or anything, just a bit of a reality check

I'm always grateful to read up stuff like this. I'm an engineer, so I love this technical stuff. But it's important for us to try not to get too caught up in it too. Always need to keep thinking back to the big picture and remembering what matters. Otherwise we'll all be broke and still make terrible music!

But on the other hand, there'll be plenty of audiophile porn for the lonely nights!