Does Sipser, perchance, have any references or a bibliography of suggested reading in his Theory of Computation text? There are a few texts listed on complexity; lots of articles.
I did come across an article by Sipser and colleagues on Arxiv:Quantum Computation by Adiabatic Evolution on arxiv.org: perhaps there are some survey articles in the references listed? Such a survey article will likely suggest a good text to start with.
This article on Arxiv came up in a search for "survey article..." @ http://arxiv.org/abs/0804.3401: Quantum Computational Complexity, by John Watrous. It could be a good start, and perhaps suggest other relevant, introductory/preliminary readings.
Sipser has an entry in Wikipedia: Sipser; it lists his research area, publications, and contact information, etc. Since you seem to like Sipser's approach, perhaps contacting him directly at MIT with your question will yield a helpful response?
Sorry I couldn't be more helpful at the moment. Akhil seems to have added a suggestion in a comment. I'll return later if I have time to expand on this.