Practical Devices XM6 features and a few queries

[kyledotroberts]

I'm fairly new to Head-fi and whilst I've always enjoyed listening to music on my PC with Sennheiser HD555's more than my iPod I never really thought much about it until stumbling across this site.
 
Since then, I'm now usually listening to my Beyerdynamic DT1350's with the XM6 which is far better than my old 555's imo.
 
Few queries about bits to do with the amp and I suppose how the headphones in general or how certain headphones can react?
 
First thing is the cross feed.
Started playing around with this for some Rage against the machine tracks that have instruments with 100% left and 0% right etc so thought I'd see how using cross feed made this any better... But actually even on the most stereo setting, the cross feed appears to increase the bass which starts to drown out other more subtle instrumentals within tracks so whilst it does seem to work for a few tracks, the vast majority now sound very bassy and I'm not sure if this is the amp, or the headphones or both together?
 
Next is the additional 75ohm impedance that you can enable.
So my DT1350's have 60ohm normally, and so I've always left this disabled so it's 60ohm's total but I was wondering if there is any benefit at all to using this switch to make my headphones basically 135ohms - would this help remove any static/noise that can be heard during quieter sections of tracks or will it not make much difference and it's just the headphones themselves that'll cause this?
 
- main reason for this question is i've been looking at the new posting around the T70 and T70P, wondering if it's worth getting the 250ohm T70 if the XM6 can drive it, and if I'd notice any benefit?
 
Other features very clear and I've been using the USB DAC with the source being my laptop which also seems pretty nice.
 
All in all, the extra parts of tracks that I'm hearing with the amp that I don't seem to get without it makes it worth grabbing and also since i take it all over very happy with the battery life, its great!
 
Hopefully these questions aren't too simplistic

 

[GreatDane]

I haven't used an XM6 but I do own the XM5. I don't know how similar the crossfeed circuitry is but my XM5 crossfeed does add a touch of bass. For most recordings I like the crossfeed/more bass effect. I use mine with the crossfeed at minimal setting.
 
The +75 Ohm feature works well for very low impedance IEMs when the source has hiss/noise. The Etymotic ER4P needs the 75 Ohms to transform into the ER4S. It won't do any harm to experiment using the +75 Ohms with any headphone. It will change the sound but most often isn't for the better(IME).
 
I have used my XM5 to drive 250 Ohms and it did a good job. It even sounds nice with 600 Ohm Beyer T1...high gain using the 634 buffer chip and AD8065 op amp.