The q701s really don't sound any warmer than k701s, they might if you compare them to eachother but in the big picture they sound the same compared to the sound signatures of different cans. The 598 is great for the price, I only had 15 or so minutes with it but especially if this will be your first quality headphone,I doubt it will disappoint you. The 598 will benefit a little from an amp (but not nearly as much as 701s) but a fiio e17 would do good for the 598, it's a amp and dac so you get a higher quality source as well plus it can be used on the go.
Are there any cheaper alternatives to the E17? The 598 may just be my first high quality headphone.