Instead of the HARX700, you should get the HAM750 which is much easier to drive. I think the HAM750 is $41 on Amazon. Instead of the Superlux HD681, you should get the Samson SR850. It is also made by Superlux, but is a better headphone. It is $40 new on Ebay with free US shipping. The JVC HAS600 is circumaural on some people, however imo the JVC HAS650 sounds much better even though it is supraaural. I think these are around $28 and $34 on Amazon.
The Koss KSC75 is bass deficient, however if you like that sound signature but with more bass then get the Koss KTXpro1. It is essentially the KSC75 with a headband instead of earhooks. The headband pressure against the ear increases the bass. The JVC HAS160 is a great headphone for around $10. I like it better than the Portapro. For around $42 on Amazon you can get the Sennheiser PX100II which is vey nice sounding, however I have a slight preference for the JVC HAS650.