BDAqua, very good idea! I think these are the relevant lines when the installation fails:
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error 19:43:09.294317 +0200 kernel Sandbox: kextd(58) System Policy: deny(1) file-write-create /private/var/db/KernelExtensionManagement/Staging/tmp.8sNiNp
default 19:43:09.294384 +0200 kextd Error making temporary directory: 1
default 19:43:09.294436 +0200 kextd Memory allocation failure.
default 19:43:09.294476 +0200 kextd Unable to stage kext (/Library/Extensions/NIUSBAudioDriver.kext) to secure location.
error 19:43:09.295440 +0200 kernel Sandbox: kextd(58) System Policy: deny(1) file-write-create /private/var/db/KernelExtensionManagement/Staging/tmp.oXkkJq
default 19:43:09.295488 +0200 kextd Error making temporary directory: 1
default 19:43:09.295545 +0200 kextd Memory allocation failure.
default 19:43:09.295588 +0200 kextd Unable to stage kext (/Library/Application Support/VirtualBox/VBoxDrv.kext) to secure location.
error 19:43:09.324577 +0200 kernel Sandbox: kextd(58) System Policy: deny(1) file-write-create /private/var/db/KernelExtensionManagement/Staging/tmp.0nEHPJ
default 19:43:09.324655 +0200 kextd Error making temporary directory: 1
default 19:43:09.324729 +0200 kextd Memory allocation failure.
default 19:43:09.324785 +0200 kextd Unable to stage kext (/Library/Application Support/VirtualBox/VBoxDrv.kext) to secure location.
default 19:43:09.324819 +0200 kextd org.virtualbox.kext.VBoxDrv was unable to stage properly; failing.
default 19:43:09.420411 +0200 deleted <private>: Successful Request
default 19:43:09.420511 +0200 deleted <private> servicePurgeable returned
default 19:43:09.420547 +0200 deleted dequeuePurge <private> [0x7fc8e4f030d0] no purges queued
default 19:43:10.407402 +0200 trustd cert[2]: AnchorTrusted =(leaf)[force]> 0
default 19:43:10.410071 +0200 authd MacOS error: -67050
default 19:43:10.421602 +0200 trustd cert[0]: ExtendedKeyUsage =(leaf)[]> 0
default 19:43:10.426897 +0200 trustd cert[1]: IntermediateEKU =(path)[]> 0
default 19:43:10.427293 +0200 Installer Trust evaluate failure: [leaf ExtendedKeyUsage] [ca1 IntermediateEKU]
default 19:43:10.450403 +0200 trustd cert[0]: ExtendedKeyUsage =(leaf)[]> 0
default 19:43:10.455483 +0200 trustd cert[1]: IntermediateEKU =(path)[]> 0
default 19:43:10.455843 +0200 Installer Trust evaluate failure: [leaf ExtendedKeyUsage] [ca1 IntermediateEKU]
default 19:43:10.478528 +0200 trustd cert[0]: ExtendedKeyUsage =(leaf)[]> 0
default 19:43:10.483704 +0200 trustd cert[1]: IntermediateEKU =(path)[]> 0
default 19:43:10.484084 +0200 Installer Trust evaluate failure: [leaf ExtendedKeyUsage] [ca1 IntermediateEKU]
default 19:43:10.506614 +0200 trustd cert[0]: ExtendedKeyUsage =(leaf)[]> 0
default 19:43:10.511575 +0200 trustd cert[1]: IntermediateEKU =(path)[]> 0
default 19:43:10.511946 +0200 Installer Trust evaluate failure: [leaf ExtendedKeyUsage] [ca1 IntermediateEKU]
default 19:43:10.562989 +0200 Installer The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
default 19:43:10.725110 +0200 coreauthd -[LAAuthenticationHintsProvider connectionInvalidated] on <private>
default 19:43:10.725229 +0200 coreauthd -[LAAuthenticationHintsProvider _deactivateWithReply:reply:] on <private>
default 19:43:10.728398 +0200 CommCenter #I handleLSNotitifcation_sync: Application exited: <private>
default 19:43:11.324544 +0200 filecoordinationd Presenter 6E66F2E3-7C34-4305-A0A9-307756515D15 detected non-coordinated event
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All I can understand is that there was a problem with the Sandbox while trying to install the kexts. There is nothing more that can help me to remove the issue, apart for "contacting the software manufacturer". Meh.
Paolo