Only the first 3 items are deducted before arriving at AGI (and therefore MAGI).
In the scenario you list here your AGI is $65,500 (80,000-5,150-7600-1,750) and your taxable income is $56,600 (65,500-8,900).
However I have a question: Why are you only contribution $7,600 to your 401k? This appears to be only 9.5%. If you double that to 19% or $15,200 your AGI drops to $57,900 which allows for a fully deductible TIRA contribution.
AGI and MAGI can be identical, or very different. MAGI has different rules for different things. I don't believe any work sponsored IRA contributions can be added back in calculating MAGI.