#1
Right from my head i have 2 jacks parralled and phms slection 4/8/16. On my cab i have 2 jacks and a mono stereo switch. 1 jack is 4 ohms mono other is 16 ohms mono, both are 8 ohms stereo.

is it possible to use both speaker cables into the cab and switch it to stereo and swtich the head to 8 ohms. or would it be 16 ohms because of the split output.

or should i just use one speaker cable into the 4 ohms jack and switch head to 4 ohms.
Equips:

Ibanez RG2550E
Jackson DKMG
ESP LTD EC 200 QM
Peavey ValveKing Head & Slant Cabinet
Peavey 5150
Ashdown Fallen Angel 4x12 Cab
Ibanez Tubescreamer TS9
#2
if you used 2 cables to the 2x 8ohm stereo jacks, it would be 4ohms your head would be seeing anyway. There really is no point though, since you don't have a true stereo head if the outputs are paralleled. I would use one cable and the 4ohm jack with the head set to 4ohm, or the 16ohm jack with your head set to 16ohm. From what some old timers told me, you're better off using the 16ohm tap since it's using all the winds on the transformer. Don't know if there is really an audible difference or not.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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#3
wouldnt running the 2 speaker cables into stereo cab make it less muddy or anything. and if it was 8 ohms stero cab id have my head at 4 ohms.
Equips:

Ibanez RG2550E
Jackson DKMG
ESP LTD EC 200 QM
Peavey ValveKing Head & Slant Cabinet
Peavey 5150
Ashdown Fallen Angel 4x12 Cab
Ibanez Tubescreamer TS9
#4
I don't think so, they are in parallel, so you're really just adding cable, which usually degrades sound more than helping it. And yes, since your amp speaker outs are in parallel, using the 2x 8ohm jacks on your cab would result in a 4ohm load your head would see.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
amp clips
amp vids