I get a strong sense that here the meaning of 'textualmente' is as it is in English, and not 'literally'.

The term 'intertextual' is pretty well established in some circles in English as meaning 'comparing two or more works'. and the use of the parenthesis indicates that the writer wants the 'inter' to be considered as either a subset or an alternative to 'textually'.

I find several uses of almost exactly this distinction in English Example: "intra- and inter-texts) [inter] textually appear in these narrative parts" (also see URL)

If you are worried about it not seeming to really make sense when opposed to an exhibit being organized 'spacially', I suggest that it has made sense to your writer, who may either be able to see something we can't, or be using language for effect rather than meaning. In this kind of writing, I sometimes see little choice but to follow where they lead.

In any case, that is my thought.

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Note added at 2 hrs (2010-11-21 17:19:31 GMT)
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I can imagine an (inter) textually organized exhibition in which some displays concentrate on a single work, while others present contrasting or complimentary works together.