That is one sweet bass! I'm so sorry you have to sell it. I'm also waiting on some SGD pickups, but it's taking forf%^kingever.
I have both a Q6 and a Q6 TBX, a 1990 and 1991 respectively. Both are great basses. The difference is that the TBX speaks differently. The low end is much bigger and it seems to have a bit more scooped mids. The neck joint adds in some midrange barkiness, I think. For the Phil thing, I think the TBX wins, but what do I know? Everytime I bring out the Modulus, even though I think it sounds great and the bombs it drops are, well, the bomb, everyone clamors for the Starfire, so that's where I live these days.
A sale is probably imminent for one of my Q6s as life has thrown some slings and arrows in my direction (medical stuff around the birth of my son. Luckily, he's escaped a myriad of issues from his hypoxic ischemic encephalopathy, essentially his lungs shredded from aspirated miconium and collapsed, leading to two heart stoppages which kept O2 from reaching his brain, from epilepsy to cerebral palsy to cognitive deficits. I still have many moments of panic where I'm brought back to that moment in the hospital.... The impact on both income and expenditures has been brutal. All worth it, Xander's an amazing 16 month old who has some skills of a 2-3 year old. He also knows bass when he hears one and will announce "That's the bass!" Pretty advanced for such a little boy! Sorry for the digression.)
But it still sucks to have to face selling gear. I'm not sure which one. The regular Q6 is a frankenstein bass with a Q6 neck added to a Q5 body. It has the best playing neck of any bass I've ever played. There are a few minor issues with the body, but it's essentially fine. The TBX has the pickups closer to the bridge than I would prefer and the neck likes slightly heavier strings than I would choose (I like light strings) to keep the neck straight, but it can be fixed by Jerry Dorsch for a couple hundred bucks (deal of the century! All new frets and planing the board). I also upgraded the preamp to a 3 band which meant I had to drill a whole and the placement choices were not the best. But it works. I'm thinking about adding in an ACG preamp I have lying around, but I want the pickups to get here first. I just can't make a decision about which one to let go. I don't know that I'd have access to a TBX again. So, the regular Q6 is perfect for what it is, while the TBX is basically a cooler bass, but has some things about its design that makes it not the best TBX for me.
OK, I'm rambling, but I've been facing this dilemma for a while now and am a bit stuck. What would you do?