I have a 508.24 and a 506, and I don't think there is a significant difference in the quantity of bass output between the two. The difference is in the upper midrange and higher frequencies. One result is that the bass will sound tighter, more tuneful and perhaps have more of an impact, but not realy louder. I will say, however, that the 508.24 or the EMC would be a meaningful upgrade. I did it and certainly dont regret spending the money on the 508.
If you like your speakers, I would look into room placement and treatment. Your speakers may sound too bright and forward because of the room. You could also talk to someone who knows tubes about the ones in your preamp.
If you like your speakers, I would look into room placement and treatment. Your speakers may sound too bright and forward because of the room. You could also talk to someone who knows tubes about the ones in your preamp.