There is target adjustment in sph-sgminer depending on the coin, this is what DM_SELECT(1, 256, 65536) does. Currently for darkcoin and myriadcoin-groestl truediffone is multiplied by 1, for quarkcoin and qubitcoin it's multiplied by 256 and for scrypt it's multiplied by 65536.
so here may be the problem - quarks should have diff1 similar as sha256 coins (so multiplier = 1)
Are you sure about this? Because for example hash of BTC block 10 (difficulty = 1) is:
000000002c05cc2e78923c34df87fd108b22221ac6076c18f3ade378a4d915e9
and hash of QRK block 600 (difficulty = 1.01576304) is:
00000096b99f154706b957c0e36cc4bf3789849e8a0684278dffac607b404641
so QRK definitely has higher target than BTC for this difficulty, otherwise this block would not be accepted. I'm not an expert in this, though.
Also take a look at:
https://github.com/bitcoin/bitcoin/blob/master/src/rpcblockchain.cpp#L36and
https://github.com/MaxGuevara/quark/blob/master/src/rpcblockchain.cpp#L31In BTC dDiff is multiplied/divided by 256 until nShift is 29 while in QRK it's multiplied/divided by 256 until nShift is 30 - so IMHO for two difficulties with the same value target value will be shifted by 8 bits.
Note that sph-sgminer displays network difficulty correctly for Quark and QubitCoin. It wouldn't be correct with wrong multiplier.