Ok gs, now I'm back and might be able to shed a little light on this for you.
First off, in my opinion you shouldn't need a multiband on anything unless there is a specific "surgical" need to do so. I like how you are experimenting with things though...but again, you're (imho) over thinking and over-processing on this.
The first thing to decide is do you want a kick drum with boom and a bass with a little more high end clack or do you want a kick that has more beater attack and a bass with more of an "ooom" type low end sound? From there, that blueprint there can help you sculpt the mix a bit better because you know what you're shooting for coming out of the gate.
In this song example you posted, I don't hear anything blatantly wrong (other than a few subjective things which I'll share in a bit) with the bass but as Geno has mentioned, the kick drum is non-existent and needs some thrust to it. See, when you create a mix, the sound of the low end on the whole comes from the relationship of the kick and bass guitar.
Together that team is what makes up the low end. Doing this to a single instrument is moot. Several instruments make up the low end in a mix and even more so in a mastered mix. It's sort of like how guys are using reference material to mix better when in reality, they are referencing mastered material. This is why so many home studio guys or newer engineers are totally getting lost and over processing trying to come up with the perfect mix. What you hear on a finished mix from a reputable engineer is NOT what you hear on the master as you know. The mix is usually flat and well balanced. It doesn't have accentuated lows etc like you've heard me mention before.
In a sense, the mix you've presented here, would *almost* be a good candidate for a mastering engineer to turn into a great final product. You need some kick drum work though and a little more tweaking to cut some of the mids you have going on here and this would be pretty good. Bass seems a bit muddy with the drive on it to me and could use more definition and a little "clack" at about 2.5 k in my opinion. It "ooms" a little too much for my liking and seems a bit too comped.
Remember when I talked about a bass with more low end and a kick with more beater etc? The low end is the toughest because you have to decide if you want a little sub low harmonic, or a major thrust. This is what YOU have to decide in this particular mix. What you choose here with the kick drum helps define your bass choices.....or in your case, if you leave the bass as is, it *should* define your kick drum.
Right now, your kick drum is doing nothing in terms of thrust. With your bass as low endy as it is, you're going to have to select a kick drum frequency that either has a little sub low harmonic in it, or a low end thrust point that is higher than the bass low end so that they don't mask.
OR, you'll need to back down some of the bass guitar lows and bring in kick drum lows. It's ok to have the bass guitar as 2nd in command of low end. Though that is usually not the classic rock way, there's nothing wrong with allowing the kick to rule the low end roost. A prime example of that is Living Color's "Cult of Personality".
http://www.youtube.com/watch?v=7xxgRUyzgs0 Give it a listen when you get a minute. You have more low end in your tune than they do....but what do you hear every time? Right...that consistent kick drum thrust. The bass is there...but you hear it more and feel it just a little. That mix sounds exactly the same on any system I listen on. That kick and bass just works so well. Take notice there is no low end kick thrust on it...yet it sounds huge and hits you in the throat instead of the stomach.
My point in sharing that......you don't need as much low end as you think to make things have impact. When the relationship works right....the stars align man. :) Now, you may not like this mix....and that's ok. But I just wanted you to hear how the opposite (kick ruling the roost) can have impact too.
In your case, you need a happy medium of kick thrust and low end on the bass. 60 Hz to 110 Hz usually gets you your thrust power with tight Q's on 50 Hz for a little sub if needed. But...you gotta be careful there because it's too easy to go over-board with it. Best to leave that stuff to an ME when it comes to the sub harms for enhancement.
If I'm you in this situation, I'm going for kick drum thrust between 60-80 Hz and will cut down/high pass the low end on the bass until it works with the kick...and I'm removing that tube thing. You've made things a bit too warm all across the board in my opinion...tube drivers etc...mask the brilliance of digital and remove the high frequencies that I personally find musically stimulating. Subjective, but that's how I'd attack it.
You made a mention in that other thread that someone from the band came to your studio and mixed a song with you telling you how much bass they wanted in things....and when they listened on their system, it had too much bass or something, right?
What were your thoughts on that mix when you listened to it on your system? If it sounded wrong to you, it was wrong. If it sounded pretty good yet sounded bad on other systems, time for monitor tuning and some room tuning. It's up to us to tell the clients "yes, I know what you want but this will not sound good sonically" when you know it will suck. Yeah, they are paying for it, but they usually don't know about this stuff like you and your name goes on it too...so it has to be a 2-way street as much as possible.
Anyway, I hope some of this helps. Keep up the great work man.
-Danny