No, DACs have been a mature technology for quite a few years now. The small measurable differences that still exist between different DACs aren't sufficient to create an audible difference. Also, you don't mention what type of connection that you're using now. If it's still a digital connection, the DACs in the player aren't being used. Possibly the output of your new player is slightly higher than your DVD player at the same setting of your receiver and the slightly higher sound level makes the sound seem more "full" although it's simply a matter of volume.
It's highly unlikely that you need a more powerful receiver than your 5002, especially at a listening distance of only about 8'. You don't mention what sound levels that you're now reaching, possibly since without an SPL meter it can't be judged accurately. The 5002 should be capable of providing peak levels of over 100dB with your 602s. If this isn't enough(although more might cause permanent hearing damage), and that's what you mean by "small", certainly a 115 watt unit isn't going to change things significantly. The difference between 90 watts and 115 watts is only about 1dB more in maximum sound level; e.g., if you now can hit 105dB on brief peaks with the 5002, this would just increase to 106dB with the new unit, a barely noticeable difference.
It isn't entirely clear what you mean exactly by "small", but it may not be anything that can be cured with floorstanding speakers. Bigger speakers don't necessarily mean bigger sound.
