This may be because the audio outputs on your television are fixed instead of variable. It may be worth checking your television's sound settings and see if you can toggle the outputs between variable and fixed. If you're connecting your television to the HD6s or D1 optically, the optical output on your TV would be a fixed output so you wouldn't be able to control the volume from the TV's remote.
More and more often TVs are using fixed outputs, making it tough to adjust the volume without hopping off the couch. Speakers like the A5+ and the HD6 feature a remote control, so you should be able to adjust the volume from their respective remotes. Speakers such as the HD3, A2+s, and original A5s can't be controlled with a remote, so one option we know of to add a remote to them is to put a preamplifier or AV receiver between your TV and speaker; that would give you a variable preamp out to connect your speakers to.