Much of the theoretically-based research in second language acquisition indicates that structures that lie at the syntax interfaces with other modules are more permeable to cross-linguistic influence (see the influential works of Sorace and her colleagues). Additionally, Tsimpli and Sorace (2006) posit that the discourse-pragmatic interface is more vulnerable to interlingual influence than the lexico-semantic interface. This paper examines the differential status of the interfaces proposed in Tsimpli and Sorace (2006) with regard to a single phenomenon—subject position in unergative and unaccusative constructions in bilingual Spanish—which allows for the study of both the syntax interface with the lexico-semantic interface (these monovalent predicates display different mappings) and the syntax interface with the discourse-pragmatic (broad and narrow focus give rise to different word order preferences). This project compares results reported in antecedent literature on subject position across predicate types and information structures in Spanish-English bilinguals (whose languages differ more in the discourse-pragmatic interface with syntax) with novel data from Spanish-Catalan bilinguals (whose languages differ more in the lexico-semantic interface with syntax). The Spanish-Catalan data were extracted from two experiments: a preference task (with 22 Catalan-Spanish bilinguals and 18 Spanish monolinguals) and a sociolinguistic interview (with two control groups: 12 Catalan speakers and 12 Spanish monolingual speakers, and two experimental groups: 12 Catalan L1 and 11 Spanish L1 bilinguals). Results indicate that while the Spanish-English bilinguals exhibit more difficulty in selecting the preferred word order across information structure contexts, as predicted by Tsimpli and Sorace (2006), the Spanish-Catalan bilinguals display more difficulty in providing the preferred word order across predicate types, contra Tsimpli and Sorace (2006). Thus, this paper concludes that language pair similarities and differences constitute a better predictor of the difficulty encountered in structures that lie at the interfaces.