The 6003 was, if I'm aligning the stars right and drinking the right potions, the model right before the Maestro, which is another 3-way.
Jensen bought out Advent, and pruduced an "upgraded" line of speakers, including the 5002/5012/anniversary Large Advent, which was a carryover from the Large advent but with a changed tweeter, one of which you'll get aguements that was an improvement, both for and against.
Also, the 6003 was built, a foray into a 3-way design. It is rumored that Advent was planning on doing this 3-way before Jensen bought 'em out, but I can't confirm nor deny this.
Later came the top-of-the-line Maestro. This was the period of the Legacy, Prodigy, ect. speakers. Jensen was in full ownership at this time, with a completely different lineup of speakers offered.
There was a smallish speaker made at this time, the Baby Advent, and Baby Advent II. I own the Baby Advent II, and find it a delightful speaker for it's diminutive size.
Maestro owners find them to be an excellent sounding speaker. I'd imagine the 6003s are the same.