Of course Xanax lowered the opiates effects !!!!
Be carefull : Quetiapine is ABSOLUTELY not recommended to combine with tramadol :
http://www.drugs.com/drug-interactions/seroquel-with-tramadol-1979-1274-2221-0.html
There is much less interaction between seroquel and codeine (it is safer)
Stay at first with codeine to feel a good buzz, i think it will be clearly better for you than tramadol
Now the good dosage (please if you take xanax what is your dosage ?)
Anyway, supposing a standard medical dosage : don't go over
0.5mg xanax, 0mg is the best !
you can try 300mg codeine with absolutely no problem !!! ( a lot of people suggest you 200-250 mg , it is a very good advice but as you take a benzo you can easy go to 300 mg (I'm "benzofan" I know what I'm talking about benzo))
e.g. crush 10 (30mg/500mg) pills and used CWE (at the final you won't really have 300mg due to lost, it is normal)
10 acetaminophen/ codeine (500/30mg) pills or 15 (400/20mg) pills are perfect
You can mix your codeine extract (very bitter) with white grappfruit juice (but absolutely not necessary, it is a small add on) to a bit potentiate a little the mixture ! AND ENJOY
SHARE WITH US YOUR FEELING, because you will feel something great !!!!

If you can avoid to mix xanax and seroquel during your codeine experiment it will be better again !!]
If you really want to stay on tramadol avoid absolutely seroquel, but as I said : --> try first with codeine you won't be disapointed
General note : don't mix tramadol and codeine it is not better