Yes you can use the Main out in stereo with your BX5 then you get a nice Stereo image when using the Stereo FX,
but you can use as example the Main Stereo out to go to FOH and you can Monitor in Stereo via Monitor out
and the Send output, therefore you have to tick the Monitor Stereo option
My aim longterm is to buy one a good quality PA speaker with a built in mixer so i can play along to mp3 tracks
There's a way that you can bring your mp3 player into the Kemper and do this without buying a mixer.
From the full 5.5 manual (page 36, at least in my pdf reader). You might read up a bit on the i/o options in general, but this would allow you to accomplish your goal without spending the extra money.
RETURN and ALTERNATIVE INPUT (4)
The ALTERNATIVE INPUT can be used as a rear-side guitar input, which is especially convenient for the Rack, and
PowerRack models. The parameter “Input Source” needs to be set accordingly in the Input Section.
The RETURN is available as balanced TRS or XLR input. While it plays a key role during PROFILING TM , as
explained in the chapter Taking a PROFILE, it can also be used in combination with the DIRECT OUTPUT/SEND to
loop in external equipment. In combination, RETURN and ALTERNATIVE INPUT can function as a pair of stereo
returns. Details can be found in the Effect Loops chapter.
Both the RETURN and the ALTERNATIVE INPUT can also be used as auxiliary inputs. You could, for instance, use
this feature to mix in music from your mp3-player and play along. You will find the corresponding mix controls in the
Output Section.
Once you go stereo for home playing, you'll never go back.
Display MoreThere's a way that you can bring your mp3 player into the Kemper and do this without buying a mixer.
From the full 5.5 manual (page 36, at least in my pdf reader). You might read up a bit on the i/o options in general, but this would allow you to accomplish your goal without spending the extra money.
RETURN and ALTERNATIVE INPUT (4)
The ALTERNATIVE INPUT can be used as a rear-side guitar input, which is especially convenient for the Rack, and
PowerRack models. The parameter “Input Source” needs to be set accordingly in the Input Section.
The RETURN is available as balanced TRS or XLR input. While it plays a key role during PROFILING TM , as
explained in the chapter Taking a PROFILE, it can also be used in combination with the DIRECT OUTPUT/SEND to
loop in external equipment. In combination, RETURN and ALTERNATIVE INPUT can function as a pair of stereo
returns. Details can be found in the Effect Loops chapter.
Both the RETURN and the ALTERNATIVE INPUT can also be used as auxiliary inputs. You could, for instance, use
this feature to mix in music from your mp3-player and play along. You will find the corresponding mix controls in the
Output Section.
I have done this. Works great.
Save up & stereo-ize your brain! Worth it! 
Save up & stereo-ize your brain! Worth it!
I ordered a second DXR-10, which should land this week. For gigs, I'll just be using one since it's only a monitor and the Kemper will go to FOH. However, when working on guitar parts in the studio I'm often dealing with backing tracks. This means either a) sit in the control room chair (which has arms, travesty of travesties!), or b) go into the live room and put in my IEMs.
It occurred to me that if I had two DXR-10s I could simply patch them into one of the stereo monitor busses and then be able to just play guitar, with bass, drums, keys and Kemper all coming out of the speakers at the appropriate rock and roll volume. Not just for fun, but because tones sound different at gig level.
Do I really need to have stereo DXR-10s when I already have IEMs and studio reference monitors?
I've learned life is better if I just ignore such silly questions. 
(which has arms, travesty of travesties!)
That's what hacksaw's are for lol.
Do I really need to have stereo DXR-10s when I already have IEMs and studio reference monitors?
Nope, not Live that's for sure!
I've learned life is better if I just ignore such silly questions.
Indeed, you're your own best advocate! 
Indeed, you're your own best advocate!
It's worth noting that I'm currently unmarried. This greatly simplifies the purchasing process.
It's worth noting that I'm currently unmarried. This greatly simplifies the purchasing process.
I wholeheartedly concur.
