No, HBOOT is only a component of the overall firmware package. Each image file inside it is responsible for a different thing. Radio is a piece, ADSP is a piece, etc.
I came here to report something positive. This will only work if you are S-OFF. It will not work at all if you are S-ON. If you need to ask what the difference is, you are S-ON.
The harman/kardon sound mod is the ADSP firmware blob. Happily, this blob also affects the display, so you get subjectively better sound while also getting a bit better backlight smoothness. It is noticable to me, I was always flipping HW Overlays off, but with this I haven't done it at all yet.
My setup, sharp panel, dev edition firmware 6.12.1540.4. This firmware comes with the DSP version 51.2.2-00593-m8974_f0.1015 that @Gurm listed despite it being lollipop, so that is also promising and honestly, I liked the DSP version in MM GPE H14 better in comparison, but the HK DSP version is better than both! If you flash the sound mod in, you will end up with a DSP version # of 62.2.2.
http://forum.xda-developers.com/htc-one-m8/development/mod-audio-hk-bs-aroma-switcher-4-1-0-t3035354
TWRP is used to install the switcher, it is very nice. You select what you have and what you want. To be clear, select HK if you want the DSP updated. If you select Boomsound it will leave you with what you already have.
Version 5 of this mod is for MM. For LP and KK you have to use older versions, but my testing with it is only with MM and only v5 has the DSP version of 62.x