Lantern,
Welcome to the forum.
Up front disclaimer, I do not ride motorcycles (only fast cars with solid audio systems), so I can only comment theoretically on 2-wheeled audio.
To answer your direct question, the
Alpine amp will replace (override) the head unit output. Total power output is solely a function of the Alpine. Your speakers will receive a maximum of
45W/ch RMS independent of the head unit's power output capability.
- The Alpine can either accept line-level (pre-amp output) or speaker level inputs (Pioneer has line-level output, Philips unknown).
To decide between the two head units, the power capability of each is
NOT important because you are adding the separate amplifier. The important head unit aspects are
user interface,
ease of use (aka button size, since you might be wearing gloves), and
feature sets.
Some ideas on these aspects:
1) I am not confident in the value of a
CD player on a motorcyle (not sure how well it would work in relation to motorcycle suspension and/or ejecting/inserting CDs while at speed)
- If not going to use the CD, then it only adds a mechanical component subject to failure.
2) If
BT from your smart phone is more useful/safer than popping in CDs (i.e. Pandora, Spotify, etc.), then the Pioneer becomes the lead dog.
3) Is the
detachable face plate important to inhibit theives? If so the Philips has it, the Pioneer appears not to.
Hope that helps a bit,
XEagleDriver