I believe what you're hearing is just bass bloat. The KSC-35s have overblown, sloppy, boomy bass that overpowers much the music, but this bass isn't impactful, slammy, or tight. In comparison, Grados have bass that is as tight as a virgin, impactful, clean, and full of slam, but it differs depending on the pads used, whether or not they've been broken in, and whether or not an amp is used.
When I auditioned the SR325 with my CHA47 at a local hifi store, I also found no presence of bass or bass impact, and my couple of buddies commented on that as well. Talking to the rep, I found out that the demo pair hadn't seen more than 15 hours of play. The stock bowl pads were of course being used, so the sound was overly bright, harsh, and sibilant.
The pair I took home are now fully broken in, and last night I spent a couple hours comparing pads. Unfortunately, I have no flats to compare. Also, these are just what I heard, so as always, YMMV.
To summarize, bowls give the least bass presence, but do give some impact when worn forward on the ear with the back edge of the pad resting on the ear (not circumaural); this tones down the highs emmensely and balances the sound more, but everything fairly distant. Everything sounds very unnatural as well.
Unmodified Senn pads give the most bass presence but the least bass impact. The covering the driver results in a drastic reduction of treble and upper mids, and the bass becomes a bit unclear and less tight, but not what I'd call sloppy. The sound darkens quite a bit and becomes soft around the edges since the foam covers the driver. Since the driver is very close to the ear, soundstage is small, separation of instruments is lacking, everything is a bit congested, and the upper mid peak around 3khz is pretty noticeable.
Modified Senn pads give a smidgen less bass presence, with a smidgen more bass impact. Uncovering the driver releases the treble, brings back the detail, and tightens the bass some. The sound is still dark, the soundstage is still small, the separation is still lacking, and the sound is still congested, but all improve in comparison to unmodified Senn pads. Upper mid peak is more noticeable.
Reversing the modified Senn pads gives, in my opinion, the best bass presence and best bass impact. I feel that the bass is the cleanest and tightest, and best of all, the soundstage separation of instruments is there, and the sounds opens up and becomes 'uncongested' in comparison to Senn pads oriented normally. The thickness of the pad sets the driver away from the ear and creates a pocket for the sound. This pocket puts space between the instruments and leaves some air for the bass to move. The presence of the highs increases, but the impact and 'tightness' of the bass and the clarity in the mids move the sound from a dark color to a bit more natural color (not to be confused with neutral, however).
Previously, I had preffered modified Senn pads with normal orientation but found problems in the balance and soundstage and such. After last nights experimentation, I found that the reversed Senn pads please me much more.
As for the difference when using an amp, Grados higher up in the line will improve more than SR60s, but they will all improve more than the KSC-35s.
Also, you may want to pick up a pair of Grados with some Senn pads, spend 100 hrs burning them in, and then spend a week or two getting your brain used to the sound, and the bass. You'll definately hear the difference in presence, balance, and impact.
