Hey JD,

As a Bass Player myself I can give you a couple different perspectives here on using more than one cabinet.

First, make sure that you are not going to overload the AMP.  I believe the HD400/750 only accept down to a

4 Ohm load so make sure the cabs are 8 ohms/ea or greater to protect your AMP.

Years back before PAs became as capable as they are today.  Bass players had to use a fairly hefty stack

if they were in any kind of good sized venue, outside or in heavily padded areas.  Now days most players

opt to have enough volume on stage (monitoring wise) and let the PA do the lifting of the stages overall volume.

That said there are still some reasons why you might want a 2nd cabinet, even when not playing in a huge venue.

1. Your PA cannot provide the extra lifting needed for Bass.

2. You cannot get your desired on-stage sound out of a single cabinet.

3. Also if you are playing in say a power-trio, you might need to have a wall of sound around you on stage to

make the song(s) appear to be "held together" better.  In other words...simply move more air !!

You WILL be able to get more volume as you load the AMP closer to the ideal impedience (4 Ohms) but that

will depend on where you set your Master and Channel Controls, too.  You will have the potential, realization

is a different issue all together.

Additionally, I use maultiple cabinets, by design.  Both for sound and because I have worn out knees, so I

choose not to have anything heavier than 50lbs...  I use both a 1-15" and a 2-10" cabinets at almost any

gig I play.  Since I have multiple AMP heads (mainly for backup purposes) I can go completely overboard

and run my entire setup with includes 2 x 1-15" cabs, 1 x 2-10" cab, 1 x 4-10" cabs for a total of 2-15s and

6-10s.  I think I have only done it a couple of times and mostly for the wall of air, rather than sheer volume !!

Keith