You’ve identified three strong contenders—Penteo, Halo, and Blackhole Immersive. Each has its strengths:

Penteo:

• Overview: Penteo is a professional upmixing tool that’s well-regarded for converting stereo to surround formats. It offers precise control over the upmixing process, allowing you to fine-tune the output to match your personal preferences.
• Capabilities: Penteo is designed for upmixing stereo audio into a wide range of formats, including 5.1, 7.1, and beyond. It uses advanced algorithms to maintain the integrity of the original mix while expanding the soundstage.
• User Experience: The interface is comprehensive, offering various presets and manual adjustments. It’s ideal if you want to dive deep into the nuances of your upmix.

Halo:

• Overview: NUGEN Audio’s Halo is another highly respected upmixing tool. It’s particularly popular in film and broadcast industries for its ability to create natural-sounding upmixes.
• Capabilities: Halo is flexible, supporting upmixing to a variety of surround formats. Its interface is intuitive, with visual tools that help you understand how the audio is being distributed across channels.
• User Experience: Halo’s user-friendly interface makes it easy to save custom presets, ensuring that you can achieve a consistent sound across your music library. It’s also known for being stable and reliable.

Blackhole Immersive:

• Overview: Eventide’s Blackhole Immersive is more recent and focuses on creative spatialization. While it’s a powerful tool, it’s more geared toward creating expansive, immersive environments rather than precise upmixing.
• Capabilities: Blackhole Immersive is not primarily a stem-based system like Penteo or Halo. It excels in creating large, ambient spaces, which might be more suited for _creative_ sound design rather than traditional upmixing.
• User Experience: If your goal is to replicate or better the effects of Pro Logic IIx and Logic7, Blackhole Immersive might not be the best fit as it doesn’t function in the same way as the other two.

Given your goal to replicate or surpass the effects of Pro Logic IIx and Logic7, Penteo and Halo are likely your best options. Penteo might give you the most control if you’re particular about the steering and placement of audio elements, while Halo provides a user-friendly interface with powerful upmixing capabilities.

Blackhole Immersive is excellent for creative sound design but may not meet your specific needs for precise upmixing. It’s more of an artistic tool than a traditional upmixer don’t you feel?

In terms of stability, both Penteo and Halo are industry-standard tools known for their reliability. With a Mac Mini or Mac Studio running these in a dedicated DAW setup, you should experience minimal issues with crashes or the need for frequent restarts.

Hope this helps, and happy listening!