Thanks for reaching out via the Bose Community. Welcome to the site!
The SA5 Amplifier is not designed for use as a 2.1 setup. Ideally, you should use either 1 or 2 pairs of speakers for the Speakers A, and Speakers B outputs.
I would recommend cross-referencing the below SA5 specifications with your speaker to confirm compatibility.
• Output Connections: Two pairs of speaker outputs (1 pair for Speakers A; 1 pair for Speakers B)
• Power Output: 100 watts per channel, nominal 8 ohms per pair
• Use only unpowered speakers. Do NOT connect any make or model of powered speakers. Doing so may cause damage to the equipment.
• One pair of speakers requires 4-ohm minimum each.
• Two pairs of speakers require 8-ohm minimum each.
If you require a user manual for the SA5, you can find one here.
I hope this helps, and if anyone else has achieved a similar setup, please feel free to add to the conversation.
Jeff G - Community Support
Feel more. Do more. Be more. Come check out my profile here. New to the community? Check out the Getting Started board. Help others find answers to your questions by clicking on 'Accept as Solution' at the bottom of a reply. If you see a post you like, make sure to give it a thumbs up!