Do hybrid slots of PXIe chassis require additional hardware (adapters etc.) to seat PXI modules?
No. The PXI Hybrid slots can accept both PXI and PXIe cards.
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I do want to point out that while hybrid slots will take PXI modules, the modules themselves need to be configure correctly. Normal PXI modules had a full backside connector. These need to be modified to be able to be inserted into a hybrid slot. The modification involves removing a portion of the connector to fit around the PXIe portion of the backplane connection.