so in my ongoing process of figuring out what gear is going to work best for me, i've been a/b'ing my svp pro, and my bddi. so i was pretty set on selling my svp for an rbi. but...i messed with some of the settings on my svp, and started getting better tones out of it. now...i bought it used, and the guy said he had it for about 4 years, and that he never retubed it. everything else is pretty much mint on/in it. the thing i like about the bddi is how "full" it sounds, and how "thick" the bottom end is on it. that's something that i've been having a problem with on the svp. well...how much difference would new preamp tubes make in this situation? will the new tubes "thicken" up the bottom end? is it worth spending the money on new tubes, or should i just get the rbi? i already go a great deal on one if i want it.