Both are Audioengine, from different ranges - so the house sound is shared and the differences are mostly in scale, engineering and price.
| Area | Better | Why |
|---|
| Bass |
evenly matched |
Much the same reach (50Hz vs 50Hz). |
| Built-in power |
evenly matched |
Similar onboard amplification (100W vs 100W RMS). |
| Connections |
A |
Audioengine HD6 adds digital inputs. |
| Size |
depends |
Audioengine A5+ Wireless is easier to place; Audioengine HD6 is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability |
depends |
Audioengine HD6: a sub output; Audioengine A5+ Wireless: a sub output. |
| Price |
B |
Audioengine A5+ Wireless is cheaper - $499 against $699, about 29% less. |
A Audioengine HD6
B Audioengine A5+ Wireless
depends neither is better in the abstract - it turns on your room, placement or how you will use them.
Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Audioengine HD6 is ahead, but only on 1 of the measured areas, and it costs about 29% more. That is a lot of money for a narrow margin on paper - Audioengine A5+ Wireless looks like the sensible buy unless something else about the Audioengine HD6 appeals to you. In a large or open-plan room, Audioengine HD6 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, Audioengine A5+ Wireless is the easier speaker to get right. Think about the whole system, not just the speakers: the roughly $200 saved by taking the cheaper pair would buy a subwoofer or a better amplifier, and either usually does more for the sound than the difference between these two.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.