The clearest and most accessible treatment of Eucharistic topics I have yet found is contained in one of the volumes of the running commentary on the Summa theologiae composed by Fr. Garrigou-Lagrange for his students at the Angelicum (including Karol Wojtyla — I wonder if we can ascertain whether these manuals were among the books Wojtyla studied during his student days). The document contains a selection of texts on, among other things, the prephilosophical or “common sense” notion of substance, the relationship of a subject to its accidents, the analysis of quantity in its various aspects (part outside of part; location and position). There are also some texts on other sacraments and on the causality of the sacraments.
Kwasniewski provided two documents, the first covering Garrigou-Langrange’s commentary on the Tertia pars, qq. 73-82 (in Word or PDF format) and another with comments of Garrigou-Langrange on the Eucharist (again, in Word or PDF format).